The sum of how many terms of the AP 8,15,22,.... Is 1490
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Step-by-step explanation:
Given
a=8
d=15-8=7
s=1490
s=n/2*[2a+(n-1)d]
1490=n/2*[16+7n-7]
=2980=n*[9+7n]
7n2+9n-2980=0
=7n2+40n+140n-2980=0
=7n(n-20)+149(n-20)=0
=(7n+149)(n-20)=0
Either
7n=-149
=n=-149/7
but n cannot be negative
so n-20=0
n=20
the answer is 20 terms
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