Pg 316(328) - Q24
This type of problem shows up relatively often. You have 9X2 + KX + 36=(3X+N)2. Go ahead and FOIL that (3X+N)2, and what you're then left with is 9X2 + KX + 36=9X2+6NX +N2. Well, that looks awfully symmetrical to me. The 9X2's cancel out; so, if we set N=6, 62 would equal 36, and that would make 6NX=36X. So, that would give K a value of 36. Well, 36-6=30 which is answer D.