check whether -120 is a term of the AP 15, 11, 7.....
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the answer is no. -120 is not in the term of the AP because
here a=15 , d=(11-15)= -4
let the nth term of the given AP be -120.then,
Tn= -120
a+(n-1)d = -120
15+(n-1)-4= -120
15-4(n-1)= -120
15-4n+4= -120
19-4n=-120
4n=-120-19
4n=-139
n= -139/4
if uhh solve this it comes in fraction.
and the no. of terms cannot be a fraction.
so, -120 is not a term of the given AP.
here a=15 , d=(11-15)= -4
let the nth term of the given AP be -120.then,
Tn= -120
a+(n-1)d = -120
15+(n-1)-4= -120
15-4(n-1)= -120
15-4n+4= -120
19-4n=-120
4n=-120-19
4n=-139
n= -139/4
if uhh solve this it comes in fraction.
and the no. of terms cannot be a fraction.
so, -120 is not a term of the given AP.
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