Question

Need help on this one

Answer 1

The trick here is to not use sin and cos at all.

The -13/15 is the x coordinate of a line from the origin to the unit circle (the line with angle theta). That happens to be the cos(theta).

The y coordinate is the sin(theta).

You can draw this as a triangle where x^2 + y^2 = 1.

So y = √(1 - (13/15)^2) ≈ 0.49889. But your exact answer should be:

$sin(\theta) = \sqrt{1-(\frac{13}{15})^2} = \frac{2\sqrt{14}}{15}$