How many integer values are there for k for which 4x^2+kxy-9y^2 is factorable?

Question

dumbcow · Answer

i say 9

anonymous · Answer

I did this problem a while back. hold on it's in my posts

anonymous · Answer

How do you get 9?

mathstudent55 · Answer

Use the ac method and factor by grouping.

ac = 4 * (-9) = -36

-36 = -1 * 36    -1 + 36 = 35
-36 = -36 * 1    -36 + 1 = -35
-36 = -2 * 18    -2 + 18 = 16
-36 = -18 * 2    -18 + 2 = -16
-36 = -3 * 12    -3 + 12 = 9
-36 = -12 * 3    -12 + 3 = -9
-36 = -4 * 9      -4 + 9 = 5
-36 = -9 * 4      -9 + 4 = -5
-36 = -6 * 6      -6 + 6 = 0

Each of the sums above in the right column is a value of k that will make this factorable.

dumbcow · Answer

i was going to let @mathstudent55 explain that :)

anonymous · Answer

http://openstudy.com/users/oldrin.bataku#/updates/51c0edaae4b0bb0a43600224

anonymous · Answer

ohh i understand now, thanks!

mathstudent55 · Answer

wlcm