Determine k, so that k2+4k+8,2k2+3k+6 and 3k2+4k+4 are three consecutive terms of an AP.
Let's take each term as a1=k2+4k+8, a2=2k2+3k+6 and a3=3k2+4k+4.
if they are terms of an AP then a2−a1=a3−a2
(2k2+3k+6)−(k2+4k+8)=3k2+4k+4−(2k2+2k+6)
2k2−k2+3k−4k+6−8=3k2−2k2+4k−2k+4−6
k2−k−2=k2+2k−2
3k=0
k=0