Question

URGENT!!! Write the product as a sum or difference.

18cos(29x)cos(17x)
Select the correct answer below:


9sin(46x)+9sin(12x)

9sin(46x)−9sin(12x)

9cos(46x)+9cos(12x)

9cos(46x)−9cos(12x)

9cos(46x)+9sin(12x)

9sin(46x)−9cos(12x)

Answer 1

9cos(46x) + 9cos(12x)

Explanation:

18cos(29x)cos(17x)

According to Product-Sum identities

cos(α)cos(β)= (1/2)[cos(α+β)+cos(α-β)]

Putting α=29x and β=17x in Product-Sum identity we get

= 18×(1/2)[cos(29x+17x)+cos(29x-1`7x)]

Dividing 18 by 2 we get 9

= 9[cos(46x)+cos(12x)]

Multiplying 9 with both the terms we get

= 9cos(46x)+9cos(12x)