Question

For what value of k will (k+9) (2k-1) and (2k+7) are consecutive terms of an a.p

Answer 1

we know that 2b=a+c
then,
2(k+9)=2k-1+2k+7
2k+18=4k+6
18-6=4k-2k
12=2k
k=6
so,
1st term=2k-1=11
2nd term=k+9=15
3rd term=2k+7=19