Question

find a,b such that 18,a,b,-3 arein a.p

Answer 1

Hi ,

Let d be the common difference of a.p

first term = 18

fourth term = a4 = -3

first term + 3d = -3

18 + 3d = -3

3d = -3 -18

3d = -21

d = -21/3

d = -7

Therefore ,

a2 - a1 = d

a - 18 = -7

a = -7 + 18

a = 11

a4 - a3 = d

-3 - a3 = -7

-3 + 7 = a3

4 = a3

Therefore ,

a = 11 ,

b = 4

I hope this helps you.

:)

Answer 2

AP -> 18, a , b , -3

Now,

Let first term be A and common difference be d

SO,

A = 18

T4 = -3 { GIVEN }

A +( n-1)d = -3

18 + 3d = -3

3d = -21

d = -7

Now,

T2 = A +( n-1)d = 18 + (-7) = 11

a = 11.

And

T3 = A + 2d = 18 + 2× (-7) = 4