Question

the first term of A.P. is -3n the 10 term is 15.find S10
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Answer 1

Step-by-step explanation:

a=-3n

a10th term=15

a+[n-9]d=15

-3n+[10-9]d=15

-3n+d=15                    

let n=10

-3[10]+d=15

-30+d=15

d=15+30

d=45

also a=-30

S10=10/2[-30+[10-1]45]

S10=5[-30+405]

S10=5[375]

S10=1875

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