Question

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which term of the AP: 3,10,17... is 120 more than its 21st term.​

Answer 1

Answer:

the given A.P is: 3,10,17....

here,

first term, a=3

and the common difference, d=7

now,

21st term of the A.P. is:

T(21)=a+(n-1)d

=a+(21-1)d

=a+20d

now, let the required term be, T(n)

then, according to question,

we have,

=> T(n)=T(21)+120

=> a+(n-1)d=a+20d+120

=> (n-1)d=20d +120

=> (n-1)d-20d=120

=> (n-1-20)d=120

=> (n-21)×7=120

=> n-21=120/7

=> n=120/7 + 21

=> n=267/7 ( n is not a natural number)

thus , there is no such term in the given AP such that it is 120 more then its 21st term.

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