Question

the third and 13 term of an A. P are - 40and 0 respectively. find the series and it's 20th term

Answer 1

Heya !!

3rd term = -40

a + 2d = -40 ------(1)

And,

13th term = 0

a + 12d = 0

a = -12d

Putting the value of a in equation (1)

a + 2d = -40

-12d + 2d = -40

-10d = -40

d = 4

And,

a = -12d = -12 × 4 = -48

First term ( a ) = -48

Second term = A + d = -48 + 4 = -44

Third term = a + 2d = -48 + 2 × 4 = -40






And,

20th term = a + 19d = -48+ 19 × 4 = -48 + 76 = 28.