Factor 4x² - 28x + 49

Here we will show you how to factor the quadratic function 4x² - 28x + 49 using the box method. In other words, we will show you how to factor 4x squared minus 28x plus 49 (4x^2 - 28x + 49) using the box method. It is a 5-step process:

Step 1: The standard form of a quadratic equation is ax² + bx + c. We start by labeling the different parts of our equation 4x² - 28x + 49, like this:

a = 4
b = -28
c = 49

Step 2: Next, we need to draw a box and divide it into four squares:

-7	-14x	49
2x	4x²	-14x
	2x	-7

We put 4x² (a) in the bottom left square and 49 (c) in the top right square, like this:

-7	-14x	49
2x	4x²	-14x
	2x	-7

Step 3: In order to fill in the other two squares, we need to do some math. We have to find two numbers that multiply together to give us the product of 4 times 49 (a × c), and add together to equal -28 (b).

More specifically, 4 times 49 is 196. Therefore, we need to find the two numbers that multiply to equal 196, and add to equal -28.

? × ? = 196
? + ? = -28

After looking at this problem, we can see that the two numbers that multiply together to equal 196, and add together to equal -28, are -14 and -14, as illustrated here:

-14 × -14 = 196
-14 + -14 = -28

Now, we can fill in the last two squares in our box with -14x and -14x. Place -14x in the upper left square, and place -14x in the lower right square.

-7	-14x	49
2x	4x²	-14x
	2x	-7

Step 4: Next, we need to find four final numbers to finish factoring our equation. We can see that our box is a 2 x 2 table made up of rows and columns.

Our goal is to find the numbers that, when multiplied together, result in the products in each square. We can do this by finding the greatest common factor in each row.

Let’s look at the top row. We have the terms -14x and 49. The greatest common factor of -14x and 49 is -7. Therefore, we write -7 to the left of the top row. You can see it here in the color green:

-7	-14x	49
2x	4x²	-14x
	2x	-7

Next, let’s look at the bottom row. We have the terms 4x² and -14x. The greatest common factor of 4x² and -14x is 2x. Therefore, we write 2x to the left of the bottom row. You can see it here in the color blue:

-7	-14x	49
2x	4x²	-14x
	2x	-7

To find the values below the table, we first divide 4x² by 2x (labeled in blue). This gives us 2x.

4x² ÷ 2x = 2x

You can see this value colored in orange below:

-7	-14x	49
2x	4x²	-14x
	2x	-7

Next, we divide -14x by 2x (labeled in blue). This gives us -7.

-14x ÷ 2x = -7

You can see this value colored in purple below:

-7	-14x	49
2x	4x²	-14x
	2x	-7

Step 5: Now we have all of the information we need to finish factoring the equation. The values outside of the box are used to factor 4x² - 28x + 49. You simply put the values on the left in one set of parentheses, and the values below in another set of parentheses, to get the answer:

(2x - 7)(2x - 7)

That’s it! Now you know how to factor the equation 4x² - 28x + 49.

Factoring Quadratics
Go here if you want to learn how to factor another quadratic function.

Factor 4x² - 27x - 81
Here is the next quadratic function on our list that we have factored for you.