Question

in an as 3rd term is 21, 9th term 63 what is the commmon difference​

Answer 1

Question-

In an A.P 3rd term is 21, 9th term is 63 ,what is the commmon difference ?

Solution-

General form of A.P. = $a_n$ = a+(n-1)d

where

• n= number of term
• d = common difference

Similarly,

$a_3$ = 21

a+(3-1) x d = 21

a+ 2d = 21. . . . (1)

$a_9$ = 63

a + (9-1) x d = 63

a + 8d = 63. . . . (2)

Subtracting eq(1) from eq(2)

a + 8d = 63

- a+ 2d = 21

--------------------

6d = 42

$d = \frac{42}{6}$

d = 7

$\therefore \sf Common \:difference \:is\: 7$