Question

In an A.P. the seventh term is 13 and 3rd term is 7. So find ‘a’ and ‘d’ in the method of elimination.

Answer 1

In an A.P. the ‘n’ th term = a_n 

= a + (n – 1) d 

Then a₇ = a + (7 – 1) d 

= a + 6d = 13 …………..(1) 

and a₃ = a + (3 – 1) d 

= a + 2d = 7 ………….. (2) 

Now solving equations (1) & (2) in elimination method

Then a + 2d = 7 

a + 2 (1.5) = 7 ⇒ a + 3 = 7 

and a = 7 – 3 = 4 

So a = 4 and d = 1.5