Clarification (1 Viewer)

[Real Madrid]

I don't really understand this question well...

What exactly am i supposed to calculate?

 

[Timothy.Siu]

7.

first n integers is

1+2+3+4+5+....+n

i guess u cud go
i.e. prove that

1+2+3+4+5+....+n=n(n+1)/2

LHS= (n+1)n/2=RHS (by using arithmetic sum)

it is a pretty pointless question.

n(n+1)/2 >210

n^2+n-420>0
(n-20)(n+21)>0
n>20

 

[jet]

I would use induction for the sum bit.

for the second bit, you say S_n > 210 and solve for n. This will give you the nth term which allows the sum to exceed the value.