Question

Cos(a+b)+cos(a+2b)+.........+cos(a+nb)

Answer 1

Step-by-step explanation:

we know that d=a2-a1

therefore we will apply the same d= cos(a+b)-cos(a+2b).

we get

(a+b) - (a+2b)

therefore

a+b - a+2b = d

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