Question

The common difference of ap is -2 find its first sum,if first term is 100and last term id -10

Answer 1

d=-2. a=100. l=-10. To find n , a_n=-10 -10=100+(n-1)(-2). -110=( n-1)(-2). n=56. Sum of terms from last = n/2(a+l). =56/2(100+(-10)).=2520