Let’s find some exact values using some well-known triangles. Then we’ll use these exact values to answer the above challenges.
sin 45°: You may recall that an isosceles right triangle with sides of 1 and with hypotenuse of square root of 2 will give you the sine of 45 degrees as half the square root of 2.
sin 30° and sin 60°: An equilateral triangle has all angles measuring 60 degrees and all three sides are equal. For convenience, we choose each side to be length 2. When you bisect an angle, you get 30 degrees and the side opposite is 1/2 of 2, which gives you 1. Using that right triangle, you get exact answers for sine of 30°, and sin 60° which are 1/2 and the square root of 3 over 2 respectively.
Now using the formula for the sine of the sum of 2 angles,
sin(A + B) = sin A cos B + cos A sin B,
we can find the sine of (45° + 30°) to give sine of 75 degrees.
We now find the sine of 36°, by first finding the cos of 36°.
The cosine of 36 degrees can be calculated by using a pentagon.
that is as much as i know about that.
