Question

If first, second and last terms of an ap are a, b, and 2a respectively, then find its sum​

Answer 1

Answer:

=3ab/2(b-a)

Step-by-step explanation:

last term is denoted by Tn=a+(n-1)d

d=b-a

2a=a+(n-1)b-a

a/b-a+1=n

n=b/b-a

sum of terms is denoted by Sn=n/2(a+Tn)

=b/2*b-a(a+3a)=3ab/2(b-a)

Answer 2

a, b......... 2a

an = a+ (n-1)d

2a = a +(n-1)(b-a)

a/b-a = n-1

a/b-a +1 = n

n = b/b-a

Sn = n/2 (a +an)

= b/ 2(b-a) *(a+2a)

=b /2(b-a) (3a)

=3ab/2(b-a )

It is the sum of this ap