I cant understand the step in which we add the equations (1) and (2) in deriving the formula of sum - Maths - Arithmetic Progressions

Question

I cant understand the step in which we add the equations (1) and
(2) in deriving the formula of sum of n terms of an AP

Ashutosh Verma · Accepted Answer

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I cant understand the step in which we add the equations (1) and (2) in deriving the formula of sum of n terms of an AP