# Can someone solve this? IGCSE MATH, SEQUENCES QUESTION Book answer= (n-8)

##
1+2+3+4+.......+#x# = #((n-8)(n-7))/2#

Write #x# in terms of #n#

1+2+3+4+.......+

Write

##### 2 Answers

Aug 8, 2018

#### Answer:

#### Explanation:

Sum of the series

and as sum is given as

comparing the two we observe that while denominator is same,

in numerator, we have two numbers

and same we have in

Hence

Aug 8, 2018

#### Answer:

Please see the explanation below

#### Explanation:

We know that the sum of natural numbers is

But it is given that

Therefore,

For this equation to be true, there is only one solution

as