Chapter 6: Problem 84
Factor. $$ 81 p^{2}-36 p q+4 q^{2} $$
Short Answer
Expert verified
The expression factors to \((9p - 2q)^2\).
Step by step solution
01
Recognize the Structure
First, notice that the expression \(81p^2 - 36pq + 4q^2\) is a quadratic trinomial with respect to \(p\). It can be expressed in the standard form \(ax^2 + bxy + cy^2\), where \(a = 81\), \(b = -36\), and \(c = 4\).
02
Check if it's a Perfect Square Trinomial
To determine if it is a perfect square trinomial, we need to check if the first and last terms are squares and the middle term is twice the product of these square roots. Here, \(81p^2\) is \((9p)^2\) and \(4q^2\) is \((2q)^2\). The middle term \(-36pq\) should equal \(-2 \times 9p \times 2q = -36pq\). Hence, this is a perfect square trinomial.
03
Factor the Trinomial
Since the trinomial is a perfect square, we can express it as the square of a binomial. Therefore, \(81p^2 - 36pq + 4q^2\) can be factored as \((9p - 2q)^2\).
04
Verify the Factorization
To ensure the accuracy of our factorization, expand \((9p - 2q)^2\):\((9p - 2q)(9p - 2q) = 81p^2 - 18pq - 18pq + 4q^2 = 81p^2 - 36pq + 4q^2\). Since this matches the original expression, our factorization is correct.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
perfect square trinomial
A perfect square trinomial is a special form of a quadratic expression. It is the result of squaring a binomial. Understanding this concept is key to factoring expressions like the one in the exercise: \(81p^2 - 36pq + 4q^2\).
A trinomial is a perfect square if:
A trinomial is a perfect square if:
- The first term is a square, such as \((9p)^2 = 81p^2\).
- The last term is a square, like \((2q)^2 = 4q^2\).
- The middle term is twice the product of the square roots of the first and last terms: \(-2 \times 9p \times 2q = -36pq\).
binomial square
Understanding a binomial square is crucial when factoring perfect square trinomials. A binomial square takes the form \((a + b)^2\), which expands to \(a^2 + 2ab + b^2\). In our example, the binomial square that simplifies to the given trinomial is \((9p - 2q)^2\).
Factorization Process:
Factorization Process:
- Identify the coefficients that form the square root of each perfect square in the trinomial: \(9p\) and \(2q\).
- Verify that the middle term matches \(2ab\), which it does in this case as \(-2 \times 9p \times 2q = -36pq\).
- The trinomial can thus be rewritten as \((9p - 2q)(9p - 2q)\), or simply \((9p - 2q)^2\).
quadratic expression
A quadratic expression is a polynomial with a degree of 2, commonly represented as \(ax^2 + bx + c\). Quadratics can usually be factored using various methods, but recognizing perfect square trinomials offers an efficient shortcut.
In the context of the given exercise, we deal with a quadratic trinomial given by \(81p^2 - 36pq + 4q^2\). Transforming this expression relies on observing its structure:
In the context of the given exercise, we deal with a quadratic trinomial given by \(81p^2 - 36pq + 4q^2\). Transforming this expression relies on observing its structure:
- The terms align perfectly as a squared set of binomial terms - indicating it's a perfect square trinomial.
- Quadratic expressions can often take different forms like \((x \pm y)^2\), perfect squares being one of the unique forms.
- By identifying this structure, we’re able to factor it smartly with less guesswork involved, resulting in \((9p - 2q)^2\).