Question 1040634
Use the formula,
{{{sin(X-Y)=sin(X)cos(Y)-cos(X)sin(Y)}}}
Substituting,
{{{sin(90-A)=sin(90)cos(A)-cos(90)sin(A)}}}
{{{sin(90-A)=1*cos(A)-0*sin(A)}}}
{{{sin(90-A)=cos(A)}}}