Question

If 18, a, b, -3 are in A.P., then a + b is equal to​

Answer 1

Step-by-step explanation:

first term (a) = 18 -------(1)

formula of A.P = a+(n-1)*d

fourth term = a+(4-1)d = a+3d ---(2)

solve (1) and (2)

a = 18

a+3d = -3

3d = 21

d= 21/3

d= 7

To find a+b

a= a+d = 18-7 = 11

b= a+2d = 18-2(7) = 18-14 = 4

so, a+b= 11+4 = 15

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