Answer:
Step-by-step explanation:
<u>The correct question is:</u> If the first, second and last term of an AP are a,b and 2a respectively, then show that the sum of all terms of an AP is 3ab/2(b-a).
Firstly, as we know that the nth term of an A.P. is given by the following formula;
, where a = first term of AP, d = common difference, n = number of terms in an AP and = last term
Since it is given that the first, second and last term of an AP are a,b and 2a respectively, that means;
first term = a
d = second term - first term = b - a
= 2a
So,
------------- [equation 1]
Now, the formula for the sum to n terms of an AP when the last term is given to us is;
{using equation 1}
Hence proved.