Question

If cos(θ)=-1/4 and θ is in the 3rd quadrant, find the exact value for
sin(θ).

Answer 1

cos (b) ^2+sin (b) ^2=1. So sine of b squared is equal to 1 minus 1/16 is equal to 15/16. And since b is in the third quadrant, sine of b is less than 0. So sine of b is equal to minus the square root of 15/16