1.

Let `a_1, a_2, a_3, ....a_n,.........`be in A.P. If `a_3 + a_7 + a_11 + a_15 = 72,` then the sum of itsfirst 17 terms is equal to :A. 153B. 306C. 612D. 204

Answer» Correct Answer - B
We have,
`a_(3)+a_(7)+a_(11)+a_(15)=72`
`rArr" "(a_(3)+a_(15))+(a_(7)+a_(11))=72`
`rArr" "2(a_(3)+a_(15))=72`
`rArr" "a_(3)+a_(15)=36rArra_(1)+a_(17)=36`
`:." "S_(17)=(17)/(2)(a_(1)+a_(17))=(17)/(2)xx36=606`


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