Question

Is there a fast way to factor 4x^2-x+18?

Answer 1

sorry is -18 not +18

Answer 2

what i do ix 4 x 18 and then try out all the multiples

but i remember there is a cross method way? i'm not sure

Answer 3

(4x-9)(x+2)

Answer 4

i know the answer..asking how to solve it in a faster way

Answer 5

i like ac method - pretty quick for all those not in the special squares categories for me

Answer 6

I learned the "bust the b" technique. I can't say that it is fast.

4 x² -1x + 18

a = 4 and c = 18 and b = -1.

The task on "bust the b" is to find numbers that mutiply to a*c AND add to b.

In this case, numbers that multiply to 4*18 and add to -1.

14 * 18 breaks aparts into the product of prime factors : 2*2*2*3*3

Look at those five factor of 14 * 18 and try to put them in the form of 2 numbers that differ by -1.

2*2*2 and 3*3 appear to differ by 1. That would be 8 and 9.

"b" has been "busted into 8 and - 9 whose sum is -1 which equals "b" in this problem.

4x - x+ 18 = 4 x² + 8 x - 9 x - 1.

The "b" has been busted.

Factoring by grouping comes next.

4 x² + 8 x - 9 x - 18 =

4x ( x + 2) - 9 ( x + 2 ) = --> On this step, (x + 2) is the common factor of the expression.

[ (x + 2) ] ( 4x - 9 ) =

( x + 2 ) ( 4x - 9)