Question

if the sum of terms in A.P. is 72, the first term is 17 and the common difference is -2. Find the no. of terms and explain the double answer.

Answer 1

Answer:

n/2(2a+(n-1)d)=72

n/2(34+(n-1)(-2))=72

n/2(34-2n+2)=72

36n-2×n×n=144

n^2-18n+72=0