If Sn denotes the sum of first n terms of an AP. Prove that S30=3(S20-

1.	If Sn denotes the sum of first n terms of an AP. Prove that S30=3(S20-S10)
Answer» LHS :- 3(S20-S10)-----iS20=20/2(2a+19d)= 10(2a+19d)20a+190d------iiSimilarly S10 =10a+45d-----iiiSubstitute ii and iii in equation i3(10a+ 145d)=30a+435dRHS :-S30 =30a+435dLHS=RHS Make equations for s 30 s 20 and s 10 separately. .....Then subtract s 20 from s 10 which will be equal to s30

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