Question

If 3rd term of an A.P. is 5 and 7th term is
13, then its common difference is :

Answer 1

Solution

Given

• 3rd terms of an A.P. is = 5
• 7th terms of an AP is = 13

Find

• Common Defference

Explanation

Let, in A.P. series

• First terms be = a
• Common difference be = d

We Know,

$\dag\boxed{\underline{\tt{\red{\:A_{n} terms\:=\:a+(n-1)d}}}}$

So, 3rd terms will be,

==> A3 = a + (2-1)d = 5

==> 5 = a + d___________(1)

Again,

==> A7 = a + (7-1)d = 13

==> 13 = a + 6d _________(2)

Subtract equ(1) & equ(2)

==> d - 6d = 5 - 13

==> -5d = -8

==> d = 8/5

Hence

• Common Defference will be d = 8/5

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