Factor completely: $5u^5 - 10u^4 - 4u^3 + 8u^2$

Question image

Understand the Problem

The question is asking us to factor the given polynomial completely. We will achieve this by first finding the greatest common factor (GCF) of all terms and factoring it out. Then, we will factor the remaining polynomial which is quadratic in nature.

Answer

$u^2(u-2)(\sqrt{5}u - 2)(\sqrt{5}u + 2)$
Answer for screen readers

$u^2(u-2)(\sqrt{5}u - 2)(\sqrt{5}u + 2)$

Steps to Solve

  1. Find the Greatest Common Factor (GCF)

Find the GCF of the coefficients: 5, 10, 4, and 8. The GCF is 1.

Find the GCF of the variable terms: $u^5$, $u^4$, $u^3$, and $u^2$. The GCF is $u^2$.

Therefore, the GCF of the entire polynomial is $1 \cdot u^2 = u^2$.

  1. Factor out the GCF

Factor $u^2$ from the polynomial $5u^5 - 10u^4 - 4u^3 + 8u^2$: $5u^5 - 10u^4 - 4u^3 + 8u^2 = u^2(5u^3 - 10u^2 - 4u + 8)$

  1. Factor by Grouping

Factor the expression inside the parenthesis, $5u^3 - 10u^2 - 4u + 8$, by grouping. Group the first two terms and the last two terms: $(5u^3 - 10u^2) + (-4u + 8)$

Factor out the GCF from each group: $5u^2(u - 2) - 4(u - 2)$

Now, factor out the common binomial factor $(u - 2)$: $(u - 2)(5u^2 - 4)$

  1. Factor the Difference of Squares

Notice that $(5u^2 - 4)$ can be written as $(\sqrt{5}u)^2 - (2)^2$, which is a difference of squares. Use the difference of squares formula $a^2 - b^2 = (a - b)(a + b)$ to factor $(\sqrt{5}u)^2 - (2)^2$: $5u^2 - 4 = (\sqrt{5}u - 2)(\sqrt{5}u + 2)$

  1. Write the Complete Factorization

Combine all the factors we found: $u^2(u - 2)(5u^2 - 4) = u^2(u - 2)(\sqrt{5}u - 2)(\sqrt{5}u + 2)$

$u^2(u-2)(\sqrt{5}u - 2)(\sqrt{5}u + 2)$

More Information

Factoring polynomials is sort of like reversing the distributive property or FOILing (First, Outer, Inner, Last) method. It's like "unpacking" a mathematical expression to reveal its building blocks!

Tips

A common mistake is not factoring completely. Always check if the remaining factors can be further factored. In this problem, students might forget to factor the difference of squares $5u^2 - 4$. Another common mistake is incorrectly applying the difference of squares formula or making sign errors during the grouping process.

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