Question

If an AP.an=5-6n.Find S15

Answer 1

Answer:

-645

Step-by-step explanation:

nth term is 15

a1= 5-6

a1= -1

an= 5- 6*15

an= 5- 90

an= -85= l

Sn= n/2(a+l)

S15= 15/2(-1+(-85))

S15= 15/2(-86)

S15= 15 × (-43)

S15= -645

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