Question

the number of terms of an AP 3,5,7_____must be taken so that the sum 120 are____​

Answer 1

Answer:

Step-by-step explanation:

10

Answer. thus there are 10 terms of the given AP must be added to get sum 120.

Answer 2

Answer:

Let's see .

3,5,7,9,11_ _ _

so the first no is considered as First term as (a) and the difference between 2nd and 1st term is taken as common difference i.e d

so, a=3 and d=5-3=2

according to the formula Sn=n/2(2a+(n-1)d)

120=n/2(6+(n-1)2)

120×2=n(6+2n-2)

240=n(2n+4)

240=2n²+4n

2n²+4n-240=0

n²+2n-120=0

n²+12n-10n-120=0

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

n=10

the number of terms will be 10-4=6 terms

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