Question

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Answer 1

Answer:

a20=126

Step-by-step- explanation:

a=12

an=?

Here, ATQ

a7 = a11-24

a+6d = a + 10d -24

12+6d = 12 + 10d -24

4d = 24

d=6

a20 = a+(n-1)d

a20 =12+(20-1)6

a20=12+19×6

a20=12+114

a20=126....

Answer 2

Answer:

let first term =a =12and common

difference =d in an AP

nth term =an =a+(n-1)d ---(1)

7th term =a7=a+6d-----(2)

a11=a+10d----(3)

given

a11-a7=24

a+10d-(a+6d)=24

a+10d-a-6d=24

4d=24

d=6--(4

required term =a20

=a+19d

=12+19*6

=12+114

=126

OR

in shortly:-

According to Question

a + 6d = a + 10d - 24

=> 4d = 24

=> d = 6

a = 12 (given)

Now

a20 = 12 + (20 - 1) 6

= 12 + 114

= 126

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