Question

If 15, k+20, 3k+15 are in AP . Find the value of k

Answer 1

a=15
a2=k+20
d=a2-a1=k+20-15 =k+5 eq 1
d=3k+15 -(k+5) =2k+10 eq2
Add 1. 2.
K+5+(2k+10)=0
K+5+2k+10=0
3k=-15
K =-5