Question

which term of ap 21,42,63,84......is210also find the sum of this ap

Answer 1

Answer:

Step-by-step explanation:

Answer 2

Answer:

Step-by-step explanation:

GIVEN AP IS: 21,42,63,84,............

HERE,

a=21 , d=21, tn= 210

WE KNOW THAT,

tn=a+(n-1)×d

210=21+(n-1)×21

210=21+21n-21

210-21=21n-21

189=21n-21

210=21n

210÷21=n

i.e n=210÷21

n=10

sn = n÷2 [2a+(n-1)d]

S10=10÷2[2×21+(10-1)21]

=10÷2[42+9×21]

=10÷2[42+189]

=10÷2×231

=1255