How do you factor the trinomial 10x^3 - 53x^2 + 70x ?

1 Answer
Apr 23, 2016

Use the AC method to get 10x^3-53x^2+70x=x(2x-5)(5x-14).

Explanation:

Right off the bat, we should notice that each term has an x in it. That means we can take an x out:
10x^3-53x^2+70x=x(10x^2-53x+70)

Now it gets a little tricky. We have the trinomial 10x^2-53x+70, and we can't simplify it any further. So we'll have work with what we have.

Factoring something like this is hard because we have that 10x^2 term. If there was no 10, it would be considerably easier to factor. To work around this, we'll use the AC method of factoring.

The first step in this method is to multiply the coefficient (the number in front of the x) of the x^2 term by the constant term (the term without an x). That means multiplying 10 and 70: 10*70=700.

Next step is finding two numbers that multiply to 700 and add to the coefficient on the x term (in this case, -53). Important to note here is that these two numbers must be negative, because their sum needs to be negative (this won't be an issue, since a negative times a negative is positive - and these two numbers must also multiply to positive 700).

Ok, first find two numbers that add to -53 and multiply to something close to 700:
-30*-23=690
-29*-24=696
-28*-25=700

We found our magic numbers: -28 and -25. Now we rewrite 10x^2-53x+70 as 10x^2-25x-28x+70. Factor out a 5x from 10x^2-25x and a -14 from -28x+70:
10x^2-53x+70=5x(2x-5)-14(2x-5)

2x-5 is a common term, so we can pull it out to get:
10x^2-53x+70=(2x-5)(5x-14)

So 10x^2-53x+70 factors into (2x-5)(5x-14). Putting this back into the first equation, we have our final result:
10x^3-53x^2+70x=x(2x-5)(5x-14)

Yes, I know this is a lot of work and is difficult to understand, but with practice you should get this method down.