Question

2. Write the sum using summation notation, assuming the suggested pattern continues.

-9 - 4 + 1 + 6 + ... + 66

Answer 1

Explanation:

a=-9

d=-4-(-9)=-4+9=5

l=66

l=a+(n-1)d

66=-9+(n-1)5

66+9=(n-1)5

n-1=75/5=15

n=15+1=16

Sn=n/2 {-18+(n-1)5}

=n/2{5n-23}

so reqd. sum is ∑[n/2{5n-23}] where n from 1→16