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Determine which polynomial is a perfect square trinomial.

A. [tex]25x^2 - 40x - 16[/tex]
B. [tex]9a^2 - 20a - 25[/tex]
C. [tex]25b^2 - 15b + 9[/tex]
D. [tex]16x^2 - 56x + 49[/tex]


Sagot :

To determine which polynomial is a perfect square trinomial, we will check each polynomial for the perfect square trinomial condition. A trinomial [tex]\(ax^2 + bx + c\)[/tex] is a perfect square trinomial if and only if [tex]\(b^2 = 4ac\)[/tex].

Let's evaluate each polynomial step by step:

1. Polynomial: [tex]\(25x^2 - 40x - 16\)[/tex]

- Here, [tex]\(a = 25\)[/tex], [tex]\(b = -40\)[/tex], and [tex]\(c = -16\)[/tex].
- Calculate [tex]\(b^2\)[/tex]:
[tex]\[ b^2 = (-40)^2 = 1600 \][/tex]
- Calculate [tex]\(4ac\)[/tex]:
[tex]\[ 4ac = 4 \cdot 25 \cdot (-16) = 4 \cdot 25 \cdot (-16) = -1600 \][/tex]
- Compare [tex]\(b^2\)[/tex] with [tex]\(4ac\)[/tex]:
[tex]\[ 1600 \neq -1600 \][/tex]
- This polynomial is not a perfect square trinomial.

2. Polynomial: [tex]\(9a^2 - 20a - 25\)[/tex]

- Here, [tex]\(a = 9\)[/tex], [tex]\(b = -20\)[/tex], and [tex]\(c = -25\)[/tex].
- Calculate [tex]\(b^2\)[/tex]:
[tex]\[ b^2 = (-20)^2 = 400 \][/tex]
- Calculate [tex]\(4ac\)[/tex]:
[tex]\[ 4ac = 4 \cdot 9 \cdot (-25) = 4 \cdot 9 \cdot -25 = -900 \][/tex]
- Compare [tex]\(b^2\)[/tex] with [tex]\(4ac\)[/tex]:
[tex]\[ 400 \neq -900 \][/tex]
- This polynomial is not a perfect square trinomial.

3. Polynomial: [tex]\(25b^2 - 15b + 9\)[/tex]

- Here, [tex]\(a = 25\)[/tex], [tex]\(b = -15\)[/tex], and [tex]\(c = 9\)[/tex].
- Calculate [tex]\(b^2\)[/tex]:
[tex]\[ b^2 = (-15)^2 = 225 \][/tex]
- Calculate [tex]\(4ac\)[/tex]:
[tex]\[ 4ac = 4 \cdot 25 \cdot 9 = 4 \cdot 225 = 900 \][/tex]
- Compare [tex]\(b^2\)[/tex] with [tex]\(4ac\)[/tex]:
[tex]\[ 225 \neq 900 \][/tex]
- This polynomial is not a perfect square trinomial.

4. Polynomial: [tex]\(16x^2 - 56x + 49\)[/tex]

- Here, [tex]\(a = 16\)[/tex], [tex]\(b = -56\)[/tex], and [tex]\(c = 49\)[/tex].
- Calculate [tex]\(b^2\)[/tex]:
[tex]\[ b^2 = (-56)^2 = 3136 \][/tex]
- Calculate [tex]\(4ac\)[/tex]:
[tex]\[ 4ac = 4 \cdot 16 \cdot 49 = 3136 \][/tex]
- Compare [tex]\(b^2\)[/tex] with [tex]\(4ac\)[/tex]:
[tex]\[ 3136 = 3136 \][/tex]
- This polynomial meets the condition for a perfect square trinomial.

Thus, the polynomial [tex]\(16x^2 - 56x + 49\)[/tex] is the perfect square trinomial among the given options.