Question

If the first, second, and last term of an AP are a, b, 2a respectively, what is its sum?

Answer 1

a+b+2a=3a+b
I guess this will be the answer

Answer 2

⚡⚡⚡$\orange{hey\:mate}$⚡⚡⚡
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.P :  a , b , . . . . . . . . . . . . . .2a

1st term= a1 = a

2nd term = a2= b

nth term = an = 2a

d = a2 - a1 = b-a

an = a1 + (n-1)d = a + (n-1)(b-a) = 2a

(n-1)(b-a) = a 

(n-1) = a / (b-a)

n = a / (b-a) + 1 =  b / ( b -a )

Sn =  n / 2    *    ( a1 +  an) =   b / 2(b-a)  *    ( a + 2a) =   3ab / 2(b-a)

⚡⚡⚡$\orange{hope\:it\:helps}$⚡⚡⚡