Mark the correct alternative in the following: If the first, second and last term of an A.P. are a, b and 2a respectively, then its sum is

Question

Philoid · Accepted Answer

Here,a₁=a;a₂=b and l=2a

Then d=a₂-a₁=b-a

So,l=a_n=a₁+(n-1)d

∴ 2a=a+(n-1)(b-a)

∴ a=n(b-a)-(b-a)

∴ a=n(b-a)-b+a

∴ n(b-a)=b

Now,

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