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How many terms of the A.P. …

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How many terms of the A.P. 3,5,7... Must be taken so that the sum is 120?
  • 2 answers

Hans Raj 6 years, 6 months ago

a=3

d=2

n=?

sn=n/2(2a+(n-1)d)=120

n/2(6+2n - 2)=120

3n+n2-n=120

n2+2n-120=0

n2+12n-10n-120=0

n(n+12) - 10(n+12)=0

n = 10

n= -12 not possible

check ur answer  s10 = 10/2(2a+18)

                                    = 5(6+18)

                                     = 5x24=120

Sneh Shrivastava 6 years, 6 months ago

a=3,d=2,n=?,An=120 So if we use the formula An=a+(n-1)d 120=3+(n-1)2 120=3+2n-2 120=1+2n 120÷2=n+1 60=n+1 60-1=n n=59
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