08-08-2014, 10:18 PM
6+24+60+120+210+336+504+720 up to 10 terms is equal to ?
a) 3680
b) 4290
c) 5720
d) 6170
answer choice b
solution
=n(n+1)(n+2)
=m^3 - m
where m = n+1
sum of all = m(m+1)(m^2+m-2)
subs m=n+1
then put n=10
=(10*11*12*13)/4
= 4290
a) 3680
b) 4290
c) 5720
d) 6170
answer choice b
solution
=n(n+1)(n+2)
=m^3 - m
where m = n+1
sum of all = m(m+1)(m^2+m-2)
subs m=n+1
then put n=10
=(10*11*12*13)/4
= 4290