Question

If 18, a, b, and -3 are in A.P, then find a+b

Answer 1

solution :

let the first term be 18

and d is the common difference

according to the series

4th term = a+3d = -3

18 + 3d = -3

d = -7

so, a = a+d

= 18-7

=11

and b = a +2d

= 18+2× -7

= 4

therefore , a+b = 11+4 = 15