# Thread: MY brain is killing me! Help guys! TRIG of Doom!

1. ## MY brain is killing me! Help guys! TRIG of Doom!

If sin x = 0.3 , cos a= 0.5 and tan b = 2.4 and x, a, b are in first quadrant find value of following:

cos ( π - x)

sin ( π - a)

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If x = π / 12 , 3 sin 2x is equal to...

?

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Help appreciated.

2. You can use the identity $\sin^2 x + \cos^2 x = 1$ to get $\cos x = \pm \sqrt{1-.3^2}$ and $\sin a = \pm \sqrt{1-.5^2}$. (Use the positive root in this case since the angles are all in the first quadrant.) Once you have these you can use the properties cos(pi-x) = -cos x and sin(pi-x) = sin x.

For the second problem just plug in the given x value and use special right triangles or special unit circle values to evaluate it. 3 sin (2pi/12) = 3 sin (pi/6) = 3 * 1/2