Question

find the 21st term of an AP whose first two terms are -3 and 4

Answer 1

Answer:

Step-by-step explanation:

12th term = 30

working: first term = a; common difference = d;

5th term: a+ (5–1)d = 16 - given ——- a+4d =16

20th term: a+ (20–1)d = 46 - given——a+19d=46

Hence we get 15 d = 30; d = 2; and a = 8.

Hence the first term of the A = 8; common difference = 2;

Hence 12th term = a + (12–1 ) d ; = a+11d = 8 + 22 = 30

Hope it will help u

Answer 2

Here,a1= -3 and a2= 4

So, d=a2-a1 , 4-(-3)=7

Now,

a21=a+20d=

-3+20×7

=-3+140=137

So, it's 21st term is 137.