Question

Use the trigonometric subtraction formula for sine to verify this identity:
sin((π / 2) – x) = cos x

Answer 1

First start by converting the angle in radians to degrees, hence will have
Sin(90-x)=cos x
=sin90cosx-cos90sinx, sin 90=1 and cos 90=0
=1(cos x)- 0(sin x)
=cos x (proved)

Answer 2

Newton's math is correct, but there is certainly no reason to convert to degrees.