Question

give answer of a question

If first term of an A.P. is a, second term is b and last term is c, then show that sum

of all terms is

(a+c)(b+c-2a)÷2(b-a)

Answer 1

a = a
second term =b
last term tn = c

D (common difference )=b-a

tn = a+(n-1)d
c =a+(n-1)(b-a)

c = a+bn -a

c =bn

c /b =n

sm = n/2( a+l)

sm = c/b/2(a+c)