Question

the sum of the series of in AP is 72 with a is 17 and d is - 2 find the number of terms and explain the double result​

Answer 1

Answer:

Step-by-step explanation: sn=72 ,a=17,d=-2

sn=n/2(2a+(n-1)d)

72=n/2(2×17+(n-1)(-2)

72=n(17+1-n)

72=18n-n^2

n^2-18n+72=0

n^2-12n-6n+72=0

n(n-12)-6(n-6)=0

n=12,6