If the sides of the Triangle are $a$, $b$ and $sqrt(a^2+ab+b^2)$, then find the value of the greatest Angle.
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If the sides of the Triangle are $a$, $b$ and $sqrt(a^2+ab+b^2)$, then find the value of the greatest Angle.
Answer Given in my notebook - $frac2pi3$ radians.
The Question is from the Chapter Solutions of Triangles and I'm aware of Sine and Cosine Rule of the triangles.
My try.
In any case, $a$ or $b$, no matter which side is greater, the 3rd side (Let's denote it by c) $ sqrt(a^2+ab+b^2) $ will have the greatest angle (i.e. greatest angle will be opposite to this side).
Now, let's take Opposite Angles of sides a, b and c as $A$, $B$, and $C$ respectively.
Then the only way to find the angle formed at angle C of the triangle can be easily calculated using Cosine Rule (if all the angles are given, which in this case is true), so putting the formula I get -
$$cos C = fraca^2+b^2-c^22ab = sqrt(a^2+ab+b^2)$$
Now, in the following case, I've to get the Value of Cosine function as $120^o or frac2pi3$ which I'm not sure how to do.
Can anyone help me with that?
Thanks :)
trigonometry triangle problem-solving
add a comment |Â
up vote
0
down vote
favorite
If the sides of the Triangle are $a$, $b$ and $sqrt(a^2+ab+b^2)$, then find the value of the greatest Angle.
Answer Given in my notebook - $frac2pi3$ radians.
The Question is from the Chapter Solutions of Triangles and I'm aware of Sine and Cosine Rule of the triangles.
My try.
In any case, $a$ or $b$, no matter which side is greater, the 3rd side (Let's denote it by c) $ sqrt(a^2+ab+b^2) $ will have the greatest angle (i.e. greatest angle will be opposite to this side).
Now, let's take Opposite Angles of sides a, b and c as $A$, $B$, and $C$ respectively.
Then the only way to find the angle formed at angle C of the triangle can be easily calculated using Cosine Rule (if all the angles are given, which in this case is true), so putting the formula I get -
$$cos C = fraca^2+b^2-c^22ab = sqrt(a^2+ab+b^2)$$
Now, in the following case, I've to get the Value of Cosine function as $120^o or frac2pi3$ which I'm not sure how to do.
Can anyone help me with that?
Thanks :)
trigonometry triangle problem-solving
1
You should have a $2$ in the denominator is your formula for the cosine.
â saulspatz
Jul 25 at 15:08
@saulspatz Thanks, but still it's difficult for me to solve
â Abhas Kumar Sinha
Jul 25 at 15:10
1
rather that the formual abouve, I think the law of cosines directly is more intiufitve. $c^2 = a^2 + b^2 - 2abcos C implies cos C = -frac 12$
â Doug M
Jul 25 at 15:27
add a comment |Â
up vote
0
down vote
favorite
up vote
0
down vote
favorite
If the sides of the Triangle are $a$, $b$ and $sqrt(a^2+ab+b^2)$, then find the value of the greatest Angle.
Answer Given in my notebook - $frac2pi3$ radians.
The Question is from the Chapter Solutions of Triangles and I'm aware of Sine and Cosine Rule of the triangles.
My try.
In any case, $a$ or $b$, no matter which side is greater, the 3rd side (Let's denote it by c) $ sqrt(a^2+ab+b^2) $ will have the greatest angle (i.e. greatest angle will be opposite to this side).
Now, let's take Opposite Angles of sides a, b and c as $A$, $B$, and $C$ respectively.
Then the only way to find the angle formed at angle C of the triangle can be easily calculated using Cosine Rule (if all the angles are given, which in this case is true), so putting the formula I get -
$$cos C = fraca^2+b^2-c^22ab = sqrt(a^2+ab+b^2)$$
Now, in the following case, I've to get the Value of Cosine function as $120^o or frac2pi3$ which I'm not sure how to do.
Can anyone help me with that?
Thanks :)
trigonometry triangle problem-solving
If the sides of the Triangle are $a$, $b$ and $sqrt(a^2+ab+b^2)$, then find the value of the greatest Angle.
Answer Given in my notebook - $frac2pi3$ radians.
The Question is from the Chapter Solutions of Triangles and I'm aware of Sine and Cosine Rule of the triangles.
My try.
In any case, $a$ or $b$, no matter which side is greater, the 3rd side (Let's denote it by c) $ sqrt(a^2+ab+b^2) $ will have the greatest angle (i.e. greatest angle will be opposite to this side).
Now, let's take Opposite Angles of sides a, b and c as $A$, $B$, and $C$ respectively.
Then the only way to find the angle formed at angle C of the triangle can be easily calculated using Cosine Rule (if all the angles are given, which in this case is true), so putting the formula I get -
$$cos C = fraca^2+b^2-c^22ab = sqrt(a^2+ab+b^2)$$
Now, in the following case, I've to get the Value of Cosine function as $120^o or frac2pi3$ which I'm not sure how to do.
Can anyone help me with that?
Thanks :)
trigonometry triangle problem-solving
edited Jul 25 at 15:09
asked Jul 25 at 15:05
Abhas Kumar Sinha
10011
10011
1
You should have a $2$ in the denominator is your formula for the cosine.
â saulspatz
Jul 25 at 15:08
@saulspatz Thanks, but still it's difficult for me to solve
â Abhas Kumar Sinha
Jul 25 at 15:10
1
rather that the formual abouve, I think the law of cosines directly is more intiufitve. $c^2 = a^2 + b^2 - 2abcos C implies cos C = -frac 12$
â Doug M
Jul 25 at 15:27
add a comment |Â
1
You should have a $2$ in the denominator is your formula for the cosine.
â saulspatz
Jul 25 at 15:08
@saulspatz Thanks, but still it's difficult for me to solve
â Abhas Kumar Sinha
Jul 25 at 15:10
1
rather that the formual abouve, I think the law of cosines directly is more intiufitve. $c^2 = a^2 + b^2 - 2abcos C implies cos C = -frac 12$
â Doug M
Jul 25 at 15:27
1
1
You should have a $2$ in the denominator is your formula for the cosine.
â saulspatz
Jul 25 at 15:08
You should have a $2$ in the denominator is your formula for the cosine.
â saulspatz
Jul 25 at 15:08
@saulspatz Thanks, but still it's difficult for me to solve
â Abhas Kumar Sinha
Jul 25 at 15:10
@saulspatz Thanks, but still it's difficult for me to solve
â Abhas Kumar Sinha
Jul 25 at 15:10
1
1
rather that the formual abouve, I think the law of cosines directly is more intiufitve. $c^2 = a^2 + b^2 - 2abcos C implies cos C = -frac 12$
â Doug M
Jul 25 at 15:27
rather that the formual abouve, I think the law of cosines directly is more intiufitve. $c^2 = a^2 + b^2 - 2abcos C implies cos C = -frac 12$
â Doug M
Jul 25 at 15:27
add a comment |Â
2 Answers
2
active
oldest
votes
up vote
2
down vote
$$cos C=fraca^2+b^2-c^22abtag1$$
as you nearly say, but $c$ is $sqrta^2+ab+b^2$. Substituting that
into $(1)$ should give you the $C$ that you want.
That's what I'm unable to do, How can you solve such equations?
â Abhas Kumar Sinha
Jul 25 at 15:09
1
No need to solve: substitute!
â Lord Shark the Unknown
Jul 25 at 15:09
Substitute what in where?
â Abhas Kumar Sinha
Jul 25 at 15:10
1
Substitute $sqrta^2+ab+b^2$ for $c$
â saulspatz
Jul 25 at 15:11
oh okay, I followed it, by mistake, I substituted that size side c, in angle C of cos..... My bad XD :)
â Abhas Kumar Sinha
Jul 25 at 15:11
 |Â
show 3 more comments
up vote
0
down vote
In Triangle ABC,
the side $c=sqrta^2+ab+b^2$ ----------------------(1)
and by cosine Rule, -
$cos C = fraca^2+b^2-c^22ab$ ------------------------------(2)
So, substituting (1) in (2) gives,
$$cos C = fraca^2+b^2-(a^2+ab+b^2)2ab$$
$$Rightarrow cos C = frac-ab2ab$$
$$iff C = 2npi pm frac2pi3$$ (for $n$ as any integer)
The rule of the Sum angle Property only stands correct only when $n=1$, thus $120^o$ or $frac2pi3$ is the reqd. answer
add a comment |Â
2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
2
down vote
$$cos C=fraca^2+b^2-c^22abtag1$$
as you nearly say, but $c$ is $sqrta^2+ab+b^2$. Substituting that
into $(1)$ should give you the $C$ that you want.
That's what I'm unable to do, How can you solve such equations?
â Abhas Kumar Sinha
Jul 25 at 15:09
1
No need to solve: substitute!
â Lord Shark the Unknown
Jul 25 at 15:09
Substitute what in where?
â Abhas Kumar Sinha
Jul 25 at 15:10
1
Substitute $sqrta^2+ab+b^2$ for $c$
â saulspatz
Jul 25 at 15:11
oh okay, I followed it, by mistake, I substituted that size side c, in angle C of cos..... My bad XD :)
â Abhas Kumar Sinha
Jul 25 at 15:11
 |Â
show 3 more comments
up vote
2
down vote
$$cos C=fraca^2+b^2-c^22abtag1$$
as you nearly say, but $c$ is $sqrta^2+ab+b^2$. Substituting that
into $(1)$ should give you the $C$ that you want.
That's what I'm unable to do, How can you solve such equations?
â Abhas Kumar Sinha
Jul 25 at 15:09
1
No need to solve: substitute!
â Lord Shark the Unknown
Jul 25 at 15:09
Substitute what in where?
â Abhas Kumar Sinha
Jul 25 at 15:10
1
Substitute $sqrta^2+ab+b^2$ for $c$
â saulspatz
Jul 25 at 15:11
oh okay, I followed it, by mistake, I substituted that size side c, in angle C of cos..... My bad XD :)
â Abhas Kumar Sinha
Jul 25 at 15:11
 |Â
show 3 more comments
up vote
2
down vote
up vote
2
down vote
$$cos C=fraca^2+b^2-c^22abtag1$$
as you nearly say, but $c$ is $sqrta^2+ab+b^2$. Substituting that
into $(1)$ should give you the $C$ that you want.
$$cos C=fraca^2+b^2-c^22abtag1$$
as you nearly say, but $c$ is $sqrta^2+ab+b^2$. Substituting that
into $(1)$ should give you the $C$ that you want.
answered Jul 25 at 15:08
Lord Shark the Unknown
84.9k950111
84.9k950111
That's what I'm unable to do, How can you solve such equations?
â Abhas Kumar Sinha
Jul 25 at 15:09
1
No need to solve: substitute!
â Lord Shark the Unknown
Jul 25 at 15:09
Substitute what in where?
â Abhas Kumar Sinha
Jul 25 at 15:10
1
Substitute $sqrta^2+ab+b^2$ for $c$
â saulspatz
Jul 25 at 15:11
oh okay, I followed it, by mistake, I substituted that size side c, in angle C of cos..... My bad XD :)
â Abhas Kumar Sinha
Jul 25 at 15:11
 |Â
show 3 more comments
That's what I'm unable to do, How can you solve such equations?
â Abhas Kumar Sinha
Jul 25 at 15:09
1
No need to solve: substitute!
â Lord Shark the Unknown
Jul 25 at 15:09
Substitute what in where?
â Abhas Kumar Sinha
Jul 25 at 15:10
1
Substitute $sqrta^2+ab+b^2$ for $c$
â saulspatz
Jul 25 at 15:11
oh okay, I followed it, by mistake, I substituted that size side c, in angle C of cos..... My bad XD :)
â Abhas Kumar Sinha
Jul 25 at 15:11
That's what I'm unable to do, How can you solve such equations?
â Abhas Kumar Sinha
Jul 25 at 15:09
That's what I'm unable to do, How can you solve such equations?
â Abhas Kumar Sinha
Jul 25 at 15:09
1
1
No need to solve: substitute!
â Lord Shark the Unknown
Jul 25 at 15:09
No need to solve: substitute!
â Lord Shark the Unknown
Jul 25 at 15:09
Substitute what in where?
â Abhas Kumar Sinha
Jul 25 at 15:10
Substitute what in where?
â Abhas Kumar Sinha
Jul 25 at 15:10
1
1
Substitute $sqrta^2+ab+b^2$ for $c$
â saulspatz
Jul 25 at 15:11
Substitute $sqrta^2+ab+b^2$ for $c$
â saulspatz
Jul 25 at 15:11
oh okay, I followed it, by mistake, I substituted that size side c, in angle C of cos..... My bad XD :)
â Abhas Kumar Sinha
Jul 25 at 15:11
oh okay, I followed it, by mistake, I substituted that size side c, in angle C of cos..... My bad XD :)
â Abhas Kumar Sinha
Jul 25 at 15:11
 |Â
show 3 more comments
up vote
0
down vote
In Triangle ABC,
the side $c=sqrta^2+ab+b^2$ ----------------------(1)
and by cosine Rule, -
$cos C = fraca^2+b^2-c^22ab$ ------------------------------(2)
So, substituting (1) in (2) gives,
$$cos C = fraca^2+b^2-(a^2+ab+b^2)2ab$$
$$Rightarrow cos C = frac-ab2ab$$
$$iff C = 2npi pm frac2pi3$$ (for $n$ as any integer)
The rule of the Sum angle Property only stands correct only when $n=1$, thus $120^o$ or $frac2pi3$ is the reqd. answer
add a comment |Â
up vote
0
down vote
In Triangle ABC,
the side $c=sqrta^2+ab+b^2$ ----------------------(1)
and by cosine Rule, -
$cos C = fraca^2+b^2-c^22ab$ ------------------------------(2)
So, substituting (1) in (2) gives,
$$cos C = fraca^2+b^2-(a^2+ab+b^2)2ab$$
$$Rightarrow cos C = frac-ab2ab$$
$$iff C = 2npi pm frac2pi3$$ (for $n$ as any integer)
The rule of the Sum angle Property only stands correct only when $n=1$, thus $120^o$ or $frac2pi3$ is the reqd. answer
add a comment |Â
up vote
0
down vote
up vote
0
down vote
In Triangle ABC,
the side $c=sqrta^2+ab+b^2$ ----------------------(1)
and by cosine Rule, -
$cos C = fraca^2+b^2-c^22ab$ ------------------------------(2)
So, substituting (1) in (2) gives,
$$cos C = fraca^2+b^2-(a^2+ab+b^2)2ab$$
$$Rightarrow cos C = frac-ab2ab$$
$$iff C = 2npi pm frac2pi3$$ (for $n$ as any integer)
The rule of the Sum angle Property only stands correct only when $n=1$, thus $120^o$ or $frac2pi3$ is the reqd. answer
In Triangle ABC,
the side $c=sqrta^2+ab+b^2$ ----------------------(1)
and by cosine Rule, -
$cos C = fraca^2+b^2-c^22ab$ ------------------------------(2)
So, substituting (1) in (2) gives,
$$cos C = fraca^2+b^2-(a^2+ab+b^2)2ab$$
$$Rightarrow cos C = frac-ab2ab$$
$$iff C = 2npi pm frac2pi3$$ (for $n$ as any integer)
The rule of the Sum angle Property only stands correct only when $n=1$, thus $120^o$ or $frac2pi3$ is the reqd. answer
answered Jul 25 at 15:26
Abhas Kumar Sinha
10011
10011
add a comment |Â
add a comment |Â
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1
You should have a $2$ in the denominator is your formula for the cosine.
â saulspatz
Jul 25 at 15:08
@saulspatz Thanks, but still it's difficult for me to solve
â Abhas Kumar Sinha
Jul 25 at 15:10
1
rather that the formual abouve, I think the law of cosines directly is more intiufitve. $c^2 = a^2 + b^2 - 2abcos C implies cos C = -frac 12$
â Doug M
Jul 25 at 15:27