Question

If in an A.P. 7th term is 108 and 11th term is 212, find the 15th term and the nth term.​

Answer 1

Answer:

a7 =108 a7= a+6d

^ a+6d =108 ----(1.)

a11= 212 a11= a+10d

^ a+10d= 212 ----(2.)

subtracting equation (1.) and (2.)

a +10d =212

- a +6d =108

after changung the signs : )

4d = 104

d= 104/4

d= 26

from eq. (1.)

a+ 6(26) =108

a+ 146 =108

a= 38

15th term >

an= a +(n-1)d

a15= 38 + (15-1)26

a15= 38 + (14)*(26)

a15= 38+ 364

a15= 402

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