SOLUTION: If cx^2 - x - 28 = (x-4)(ax + b) , what is the value of c?

Algebra ->  Test -> SOLUTION: If cx^2 - x - 28 = (x-4)(ax + b) , what is the value of c?      Log On


   

Question 1089861: If cx^2 - x - 28 = (x-4)(ax + b) , what is the value of c?
Answer by Edwin McCravy(20054) About Me  (Show Source):
You can put this solution on YOUR website!
An easier way to do these problems than the way I showed you before
is to substitute "smart" numbers for x:

cx%5E2+-+x+-+28%22%22=%22%22%28x-4%5E%22%22%29%28ax%5E%22%22+%2B+b%29

The "smart" number to substitute for x is 4.  That's because if we
are "smart", we will observe the (x-4) factor, and immediately know
that if we substitute x=4, the (x-4) will become 0, which will make 
the entire right side 0

c%284%29%5E2+-+4+-+28%22%22=%22%22%284-4%5E%22%22%29%28a%284%29%5E%22%22+%2B+b%29

16c+-+32%22%22=%22%220%29

16c%22%22=%22%2232%29

c%22%22=%22%222

And we need go no further, for that's all we were asked for!

Edwin