Question

the fiffth term of an ap is 1 and the 31st term is -77.which term of ap is -17

Answer 1

A+4D=1. (fifth term is 5 and 31st term is -77)
A+30D= -77

By elimination
A+4d=1
A+30d=-77
- - +
_________
-26d=78
d=78/-26
D= -3


A+4d=1
A+4(-3)=1
A-12=1
A=13


An= A+ (n-1)D
-17= 13+(n-1)-3
-17-13=-3n+3
-30-3=-3n
-33/3=-n
-11= -n
N= 11

Hence it's 11 th term will be -17


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