The incorrect step is Step 4, cos (π/2 -x) cos(-y) + sin (π/2 -x)sin(-y), the correct option is C.
Trigonometric Identities are based on the trigonometric ratios used to solve Trigonometric equations.
The steps used to solve the trigonometric identity are :
Step 1 : sin(x+y)
Step 2: cos ((π/2) - (x+y))
Step 3 : cos ( (π/2 -x) -y)
Step 4 : cos (π/2 -x) cosy + sin (π/2 -x)siny
Step 5: sinxcosy+cosxsiny
Therefore,the correct step is cos (π/2 -x) cosy + sin (π/2 -x)siny and not cos (π/2 -x) cos(-y) + sin (π/2 -x)sin(-y) , the incorrect step is Step 4.
The complete question is attached with the answer.
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