Factor -100x² - 99x

Factor -100x² - 99x - 18

Here we will show you how to factor the quadratic function -100x² - 99x - 18 using the box method. In other words, we will show you how to factor negative 100x squared minus 99x minus 18 (-100x^2 - 99x - 18) using the box method. It is a 5-step process:

Step 1: The standard form of a quadratic equation is ax² + bx + c. In this equation, a is negative. Therefore, we need to start by setting aside the negative (-). We do this by flipping the signs in the equation to get 100x² + 99x + 18. Now we can label the different parts of our equation, like this:

a = 100
b = 99
c = 18

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

6	24x	18
25x	100x²	75x
	4x	3

We put 100x² (a) in the bottom left square and 18 (c) in the top right square, like this:

6	24x	18
25x	100x²	75x
	4x	3

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 100 times 18 (a × c), and add together to equal 99 (b).

More specifically, 100 times 18 is 1800. Therefore, we need to find the two numbers that multiply to equal 1800, and add to equal 99.

? × ? = 1800
? + ? = 99

After looking at this problem, we can see that the two numbers that multiply together to equal 1800, and add together to equal 99, are 24 and 75, as illustrated here:

24 × 75 = 1800
24 + 75 = 99

Now, we can fill in the last two squares in our box with 24x and 75x. Place 24x in the upper left square, and place 75x in the lower right square.

6	24x	18
25x	100x²	75x
	4x	3

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 24x and 18. The greatest common factor of 24x and 18 is 6. Therefore, we write 6 to the left of the top row. You can see it here in the color green:

6	24x	18
25x	100x²	75x
	4x	3

Next, let’s look at the bottom row. We have the terms 100x² and 75x. The greatest common factor of 100x² and 75x is 25x. Therefore, we write 25x to the left of the bottom row. You can see it here in the color blue:

6	24x	18
25x	100x²	75x
	4x	3

To find the values below the table, we first divide 100x² by 25x (labeled in blue). This gives us 4x.

100x² ÷ 25x = 4x

You can see this value colored in orange below:

6	24x	18
25x	100x²	75x
	4x	3

Next, we divide 75x by 25x (labeled in blue). This gives us 3.

75x ÷ 25x = 3

You can see this value colored in purple below:

6	24x	18
25x	100x²	75x
	4x	3

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 -100x² - 99x - 18. You simply put the values on the left in one set of parentheses, and the values below in another set of parentheses, to get:

(25x + 6)(4x + 3)

In our original quadratic equation, -100x² - 99x - 18, a is negative. Therefore, we need to add a negative (-) sign before our two sets of parentheses, like this:

-(25x + 6)(4x + 3)

That’s it! Now you know how to factor the equation -100x² - 99x - 18.

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