Use the sum-to-product formulas to rewrite the sum or difference as a product.
A)
B)
C)
D)

Question

Use the sum-to-product formulas to rewrite the sum or difference as a product. ​  ​
A)​ 
B)​ 
C)​ 
D)​

Quizplus · Accepted Answer

The sum-to-product formula for sine is: sin(a) + sin(b) = 2sin((a+b)/2)cos((a-b)/2)
Applying this formula to the given expression:
sin(20) + sin(40) = 2sin((20+40)/2)cos((40-20)/2) = 2sin(30)cos(10) = 2(1/2)(cos(10)) = cos(10)
Therefore, the expression can be rewritten as cos(10), which is equivalent to option D.

Use the Sum-To-Product Formulas to Rewrite the Sum or Difference