Question

If a rectangle has an area of x^2+x-20 and a width of x-4, what is the length?

Answer 1

Answer:

This (x - 5) represents the length of the rectangle.

Step-by-step explanation:

The formula for the area of a rectangle of length L and width W is A = L * W.

Here, the width is x - 4 and the area is x^2 + x - 20.  Dividing the width (x - 4) into the area results in an expression for the length:

x - 4  /   x^2 + x - 20

Let's use synthetic division here.  It's a little faster than long division.

If the divisor in long division is x - 4, we know immediately that the divisor in synthetic division is 4:

4   /   1    1    -20

              4     20

    --------------------

         1     5     0

This synthetic division results in a remainder of 0.  This tells us that 4 (or the corresponding (x - 4) is indeed a root of the polynomial x^2 + x - 20, and so *(x - 4) is a factor.  From the coefficients 1 and 5 we can construct the other factor:  (x - 5).  This (x - 5) represents the length of the rectangle.