Question

find the value of x if 12 term of the A.P x-7,x-2,x+3,........81 find S12 also

Answer 1

nth term in an ap is a+(n-1)d, where a is the first term in an ap and d is the common difference between two successive terms.

here, 1st term is x-7,difference is 5 and 12th term is 81 which implies
( x-7)+(12-1)5=81
(x-7)+11(5)=81
(x-7)+55=81
(x-7)=26
x=33

Sn = n/2(a+an), where Sn is sum of n terms in an ap

here, an = 12th term=81,that implies
S12=12/2(x-7+81),where x=33
S12=6(107)=642

Answer 2

Answer:

Step-by-step explanation:

nth term in an ap is a+(n-1)d, where a is the first term in an ap and d is the common difference between two successive terms.

here, 1st term is x-7,difference is 5 and 12th term is 81 which implies

( x-7)+(12-1)5=81

(x-7)+11(5)=81

(x-7)+55=81

(x-7)=26

x=33

Sn = n/2(a+an), where Sn is sum of n terms in an ap

here, an = 12th term=81,that implies

S12=12/2(x-7+81),where x=33

S12=6(107)=642

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