How do you multiply \frac { x - 4} { 4x ^ { 2} + 10x } \cdot \frac { 4x ^ { 3} + 10x ^ { 2} } { 2x ^ { 2} }x44x2+10x4x3+10x22x2?

1 Answer
Apr 24, 2017

(x-4)/(2x)x42x

Explanation:

When multiplying fractions we simply multiply across.
Let's start with the numerators.

(x-4)(4x^3+10x^2)(x4)(4x3+10x2)

Remember we multiply every term with each other.
So,

(x*4x^3)+(x*10x^2)+(-4*4x^3)+(-4*10x^2)(x4x3)+(x10x2)+(44x3)+(410x2)

4x^4+10x^3-16x^3-40x^24x4+10x316x340x2

[Simplify common variables]

4x^4color(red)(+10x^3-16x^3)-40x^24x4+10x316x340x2

4x^4-6x^3-40x^24x46x340x2

color(blue)"Now we do the same for the denominators"Now we do the same for the denominators

(4x^2+10x)(2x^2)(4x2+10x)(2x2)

(4x^2*2x^2)+(10x*2x^2)(4x22x2)+(10x2x2)

8x^4+20x^38x4+20x3

So now we have...
our numerator
4x^4-6x^3-40x^24x46x340x2

and our denominator
8x^4+20x^38x4+20x3

(4x^4-6x^3-40x^2)/(8x^4+20x^3)4x46x340x28x4+20x3

Now look for common factors to simplify our fraction.
I found 2x^22x2 in the numerator and 4x^34x3 in the denominator

(2x^2(2x^2-3x-20))/(4x^3(2x+5))2x2(2x23x20)4x3(2x+5)

Divide our common factor

((2x^2-3x-20))/(2x(2x+5))(2x23x20)2x(2x+5)

(2x^2-3x-20)/(2x(2x+5)2x23x202x(2x+5)

Factor the numerator using whatever method your prefer.
[Look here if you are confused on how I factored the numerator.](https://www.mathsisfun.com/algebra/factoring-quadratics.html)
Your result should be

((x-4)(2x+5))/(2x(2x+5)(x4)(2x+5)2x(2x+5)

((x-4)cancel((2x+5)))/(2xcancel((2x+5))

(x-4)/(2x)