Find the sum of 20 terms of the AP (x+y) , (x-y) , (x -3y),…., – InterviewSolution

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1.	Find the sum of 20 terms of the AP (x+y) , (x-y) , (x -3y),….,
Answer» Correct Answer - 20(x-18y) a=(x+y) and d= ( x-y) -(x +y) =-2y ` S_(20)= 20/2 x [2a +(20-1)d] = 10xx [2(x+y)+190xx(-2y)] = 20 (x-18y)`

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