8th term of an AP is40. Calculate the sum of first 15terms

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Solution

8-th term of ap =40
first term =a
common difference=d
a+7d= 40
sum to n terms of an ap =(n/2) [2a+(n-1)d]
Sum of 15 term =(15/2)[2a+(15-1)d]
=(15/2)[2a+14d]
=(15/2)[2(a+7d)]
=(15/2)[2×40]
=15×40
=600
hope you understand.all the best

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8th term of an AP is40. Calculate the sum of first 15terms

8-th term of ap =40 first term =a common difference=d a+7d= 40 sum to n terms of an ap =(n/2) [2a+(n-1)d] Sum of 15 term =(15/2)[2a+(15-1)d] =(15/2)[2a+14d] =(15/2)[2(a+7d)] =(15/2)[2×40] =15×40 =600 hope you understand.all the best

8-th term of ap =40
first term =a
common difference=d
a+7d= 40
sum to n terms of an ap =(n/2) [2a+(n-1)d]
Sum of 15 term =(15/2)[2a+(15-1)d]
=(15/2)[2a+14d]
=(15/2)[2(a+7d)]
=(15/2)[2×40]
=15×40
=600
hope you understand.all the best