# Math Help - sin(A+B) and cos rule

1. ## sin(A+B) and cos rule

Solving using sin(A+B) and cos rule
Can someone show each od the steps and answer for this question. It will give something to work off for the rest of them. Very much appreciated

1) Using the identities for sin(A+B) and cos^2(theta)+sin^2(theta)=1.

Find sine 65 degrees, given that sin 40(degrees)=0.643 and sin 25(degrees)=0.423?

2. $\cos{25^o} = \sqrt{1 - \sin^2{25^o}}$

$\cos{40^o} = \sqrt{1 - \sin^2{40^o}}$

$\sin{65^o} = \sin{(40^o + 25^o)} = \sin{40^o}\cos{25^o} + \cos{40^o}\sin{25^o}$

Substitute the values and find the required result.

3. ## Finding Cos

So i'm sorry this probablyreally basic for you but i'm new to trig.

To find Cos 25 = you find the square root of 1 - sin^2 25 degrees.

How do you calculate sin^2 25degrees

4. Originally Posted by GAVREED2
How do you calculate sin^2 25degrees
you were given $\sin(25^\circ) = 0.423$

$\sin^2(25^\circ) = (0.423)^2$