Question

12. If 18, a, b,- 3 are in AP , then find a + b.​

Answer 1

Given,

Given terms are = 18,a,b and -3

The given terms are in AP.

To find,

The value of the (a+b) term.

Solution,

The given terms are in AP, so the common difference between any two consecutive terms will be always equal.

From the above mentioned mathematical statement, we can establish the following mathematical equation.

Second term - First term = Fourth term - Third term

a-18 = -3-b [By putting values.]

a+b = -3+18

a+b = 15

Hence, the value of the term (a+b) is 15.

Answer 2

Let p, be the first term i.e; 18

And, d, be the common difference,

From given series,

4th term =p+3d=−3

⟹18+3d=−3

Hence, d=−7

So, a=p+d=18−7=11

And, b=p+2d=18−14=4

Therefore,

a+b=11+4=15