C2 maths help

man111111

Given that x is an acute angle and sin x =12/13, use the identity cos^2 x + sin^2 x= 1 to show that 13cos x =5.

Reply 1

Apachai Hopachai

Original post by man111111

Given that x is an acute angle and sin x =12/13, use the identity cos^2 x + sin^2 x= 1 to show that 13cos x =5.

Cool, let's work through this.

Do you know what an acute angle is? An angle between 0 and 90 degrees.

So,

sin(0<x<90)=\frac{12}{13}

(\sin x)^2 = \frac{144}{169}

1 - (\cos x)^2 = \frac{144}{169}

Can you finish?

Reply 2

man111111

Original post by Apachai Hopachai

Cool, let's work through this.

Do you know what an acute angle is? An angle between 0 and 90 degrees.

So,

sin(0<x<90)=\frac{12}{13}

(\sin x)^2 = \frac{144}{169}

1 - (\cos x)^2 = \frac{144}{169}

Can you finish?

Hi, thanks for replying. I don't know how to finish it?
Is (cos x)^2 the same as cos^2 x

Reply 3

RDKGames

Study Forum Helper

Original post by man111111

Hi, thanks for replying. I don't know how to finish it?
Is (cos x)^2 the same as cos^2 x

Yes it is. NOW do you know how to finish?

Reply 4

man111111

Original post by RDKGames

Yes it is. NOW do you know how to finish?

Hi thanks for replying. I don't know how to finish it.

Reply 5

RDKGames

Study Forum Helper

Original post by man111111

Hi thanks for replying. I don't know how to finish it.

Okay.....

If you say

Y=\cos(x)

then your equation becomes

1-Y^2=\frac{144}{169}

and you want to solve for Y.

Is this clearer...?

Reply 6

Apachai Hopachai

Original post by man111111

Hi thanks for replying. I don't know how to finish it.

This is not food, you can't just throw it in the bin if you can't finish it.

FINISH IT

Reply 7

man111111

Original post by RDKGames

Okay.....

If you say

Y=\cos(x)

then your equation becomes

1-Y^2=\frac{144}{169}

and you want to solve for Y.

Is this clearer...?

Thank you for helping me.

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