Write the product as a sum or difference. Write the product as a sum or difference. sin x/7 cos 8x/7 Solution sin(x/7)cos(8x/7) sinA - sinB=2cos(A+B)/2 sin(A-B)/2 1/2(sinA -sinB)= sin(A-B)/2 cos (A+B)/2 comparing the given expression with the above formula we get A-B/2=x/7 and A+B/2=8x/7 A-B=2x/7 and A+B= 16x/7 A=9x/7 and B = x Therefore the required expression is sin(9x/7)/2 -sinx/2.

1. Write the product as a sum or difference. Write the product as a sum or difference. sin x/7 cos
8x/7
Solution
sin(x/7)cos(8x/7)
sinA - sinB=2cos(A+B)/2 sin(A-B)/2
1/2(sinA -sinB)= sin(A-B)/2 cos (A+B)/2
comparing the given expression with the above formula we get
A-B/2=x/7 and A+B/2=8x/7
A-B=2x/7 and A+B= 16x/7
A=9x/7 and B = x
Therefore the required expression is
sin(9x/7)/2 -sinx/2