Question

find the 1st 3 TERMS OF AN AP OF 3rd TERM 11 AND SUM OF 1st 3 TERMS 21

Answer 1

1st term = a
Second term = a + d
Third term = a + 2d

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Here,

Third term = 11

a + 2d = 11

a = 11 - 2d ----1equation

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Sum of 1st 3 term = 21

a + a +d + a + 2d = 21

Putting the value of a from 1equation,

11 - 2d + 11- 2d + d + 11- 2d + 2d = 21

=> 33 -3d = 21

=> 33 - 21 = 3d

=> 12 = 3d

=> 12/3 = d

=> 4 = d


Putting the value of d in 1equation,


a = 11 - 2d

a = 11 - 2(4)

a = 11 - 8

a = 3


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3 terms of ap are:-

a = 3
a + d = 3 + 4 = 7
a +2d = 3+8 = 11



I hope this will help you

-by ABHAY