Question

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

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Answer 1

Answer of ur ques is- 3ab / 2(b-a)

A.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)

Answer 2

Answer:

The first , second and the last terms of an A.P. are a ,b , c respectively. Prove that the sum is ((a+c)(b+c-2a)),(2(b-a)) .