Factor 18x² + 91x + 76

Here we will show you how to factor the quadratic function 18x² + 91x + 76 using the box method. In other words, we will show you how to factor 18x squared plus 91x plus 76 (18x^2 + 91x + 76) 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 18x² + 91x + 76, like this:

a = 18
b = 91
c = 76

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

19	19x	76
18x	18x²	72x
	x	4

We put 18x² (a) in the bottom left square and 76 (c) in the top right square, like this:

19	19x	76
18x	18x²	72x
	x	4

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 18 times 76 (a × c), and add together to equal 91 (b).

More specifically, 18 times 76 is 1368. Therefore, we need to find the two numbers that multiply to equal 1368, and add to equal 91.

? × ? = 1368
? + ? = 91

After looking at this problem, we can see that the two numbers that multiply together to equal 1368, and add together to equal 91, are 19 and 72, as illustrated here:

19 × 72 = 1368
19 + 72 = 91

Now, we can fill in the last two squares in our box with 19x and 72x. Place 19x in the upper left square, and place 72x in the lower right square.

19	19x	76
18x	18x²	72x
	x	4

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 19x and 76. The greatest common factor of 19x and 76 is 19. Therefore, we write 19 to the left of the top row. You can see it here in the color green:

19	19x	76
18x	18x²	72x
	x	4

Next, let’s look at the bottom row. We have the terms 18x² and 72x. The greatest common factor of 18x² and 72x is 18x. Therefore, we write 18x to the left of the bottom row. You can see it here in the color blue:

19	19x	76
18x	18x²	72x
	x	4

To find the values below the table, we first divide 18x² by 18x (labeled in blue). This gives us x.

18x² ÷ 18x = x

You can see this value colored in orange below:

19	19x	76
18x	18x²	72x
	x	4

Next, we divide 72x by 18x (labeled in blue). This gives us 4.

72x ÷ 18x = 4

You can see this value colored in purple below:

19	19x	76
18x	18x²	72x
	x	4

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 18x² + 91x + 76. 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:

(18x + 19)(x + 4)

That’s it! Now you know how to factor the equation 18x² + 91x + 76.

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