Question

The sum of how many terms of an AP 815,22...is1490

Answer 1

Step-by-step explanation:

a=8

d=7

Sn=1490

n=?

Sn=n/2{2a+(n-1)d}

1490=n/2{2*8 +(n-1)*7}

1490=n/2{16+7n - 7}

1490=n/2{9 +7n}

1490=4.5n + 3.5n²

3.5n² +4.5n - 1490= 0

By solving the roots u will get the answer.

n will get 2 values one of which will be negative take the value which is positibe as n cant be negative.

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