Chapter 4: Problem 8
Factor completely. \(20 x^{4}+60 x^{3}-5 x^{2}-15 x\)
Short Answer
Expert verified
The complete factorization is \(5x(2x - 1)(2x + 1)(x + 3)\).
Step by step solution
01
Identify Common Factors
Look at each term in the polynomial to find the greatest common factor (GCF). The terms are: \(20x^4\), \(60x^3\), \(-5x^2\), and \(-15x\). The GCF is \(5x\), since each term is divisible by 5 and contains at least one \(x\).
02
Factor Out the GCF
Factor \(5x\) out of each term in the polynomial: \[20x^4 + 60x^3 - 5x^2 - 15x = 5x(4x^3 + 12x^2 - x - 3)\].
03
Group Terms in Pairs
Focus on the expression inside the parentheses: \(4x^3 + 12x^2 - x - 3\). Group the terms: \((4x^3 + 12x^2) + (-x - 3)\).
04
Factor Each Group
Factor out the greatest common factor from each group: \(4x^2(x + 3) - 1(x + 3)\).
05
Factor by Grouping
Notice that \((x+3)\) is common in both groups. Factor \((x+3)\) out: \((4x^2 - 1)(x + 3)\).
06
Factor the Difference of Squares
Recognize \((4x^2 - 1)\) as a difference of squares: \((2x)^2 - (1)^2\). Factor it further: \((2x - 1)(2x + 1)\).
07
Combine All Factors
Combine the factors obtained: \[5x(2x - 1)(2x + 1)(x + 3)\].
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Greatest Common Factor
When factoring polynomials, it's crucial to first identify the Greatest Common Factor (GCF). The GCF is the largest factor that divides all the terms in the polynomial.
For the expression given in our problem, the terms are 20x鈦, 60x鲁, -5x虏, and -15x. Notice how each of these terms has a factor of 5 and at least one x.
By factoring the GCF, you're basically pulling out the common 'block' that each term in the polynomial shares. In our example, this results in taking out 5x to get: 5x(4x鲁 + 12x虏 - x - 3). This is a fundamental step that sets the stage for more advanced factoring techniques!
For the expression given in our problem, the terms are 20x鈦, 60x鲁, -5x虏, and -15x. Notice how each of these terms has a factor of 5 and at least one x.
- 20x鈦 can be divided by 5x, resulting in 4x鲁.
- 60x鲁 divided by 5x gives us 12x虏.
- -5x虏 divided by 5x leaves us with -x.
- -15x divided by 5x simplifies to -3.
By factoring the GCF, you're basically pulling out the common 'block' that each term in the polynomial shares. In our example, this results in taking out 5x to get: 5x(4x鲁 + 12x虏 - x - 3). This is a fundamental step that sets the stage for more advanced factoring techniques!
Difference of Squares
The difference of squares is a special pattern in polynomials that comes in handy while factoring. It is expressed as:
\[ a^2 - b^2 = (a + b)(a - b) \]
Finding this pattern can significantly shorten the factoring process. In our example, after simplifying using GCF and grouping, we get: (4x虏 - 1)(x + 3), where 4x虏 - 1 is a difference of squares.
Recognizing the difference of squares is a key skill and can sometimes be overlooked, so keeping an eye out for perfect squares can save time and effort!
\[ a^2 - b^2 = (a + b)(a - b) \]
Finding this pattern can significantly shorten the factoring process. In our example, after simplifying using GCF and grouping, we get: (4x虏 - 1)(x + 3), where 4x虏 - 1 is a difference of squares.
- Recognize that 4x虏 is (2x)虏 and 1 is 1虏. This gives us: (2x)虏 - 1虏.
- Applying the difference of squares formula, it factors into: (2x - 1)(2x + 1).
Recognizing the difference of squares is a key skill and can sometimes be overlooked, so keeping an eye out for perfect squares can save time and effort!
Factor by Grouping
Factor by grouping is a handy tool when dealing with polynomials with four or more terms. This method involves grouping terms that have common factors.
In the expression 4x鲁 + 12x虏 - x - 3, we look at it in pairs to see if there鈥檚 anything we can factor out.
By factoring out (x + 3), you simplify further to get: (4x虏 - 1)(x + 3).
This strategy can take a longer polynomial and break it down into factors that are more straightforward to handle or recognize with other methods such as the difference of squares.
The beauty of the factor by grouping approach is that it allows you to deal with polynomials that might not have easily recognizable patterns at first glance, providing a stepping stone to more complex problems.
In the expression 4x鲁 + 12x虏 - x - 3, we look at it in pairs to see if there鈥檚 anything we can factor out.
- For (4x鲁 + 12x虏), the common factor is 4x虏, giving us 4x虏(x + 3).
- For (-x - 3), the common factor can be considered as -1, leading to -1(x + 3).
By factoring out (x + 3), you simplify further to get: (4x虏 - 1)(x + 3).
This strategy can take a longer polynomial and break it down into factors that are more straightforward to handle or recognize with other methods such as the difference of squares.
The beauty of the factor by grouping approach is that it allows you to deal with polynomials that might not have easily recognizable patterns at first glance, providing a stepping stone to more complex problems.