Simplifying Trigonometric Expressions

Simplify each trig expressions.

(1) cos[(3pi/2) + A)

(2) sin(A - pi)

(1) cos[(3pi/2) + A)] = cos[(-pi/2) + A)] = sinA
or
cos[(3pi/2) + A)] = -sin(3pi/2)sinA = sinA

(2) sin(A - pi) = sinA cospi = -sinA

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cos[(3pi/2) + A) = sin A

sin(A - pi) = - sin A