Question : The 13th term from the end of the A.P. : 20, 13, 6, -1, . . .,-148 is:
a) 57
b) -57
c) 64
d) -64
Doubt by Vikrant
Solution :
20, 13, 6, -1, . . .,-148
a=20
a=20
l=-148
d=a2-a1
d=13-(20)
d=-7
n=13
d=a2-a1
d=13-(20)
d=-7
n=13
We know, the nth term of the AP from the end is given by
an = l-(n-1)d
where l is the last term and d is the common difference of the AP.
an = l-(n-1)d
where l is the last term and d is the common difference of the AP.
a13=-148-(13-1)(-7)
a13=-148+7(12)
a13=-148+84
a13=-64
a13=-148+7(12)
a13=-148+84
a13=-64
The 13th term from the end of the AP is -64.
Hence, d)-64 is the correct option.