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Math

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PROBLEM

Quadratic Formula
Solve for x .
x25x24=0x=[?]\begin{array}{c} x^{2}-5 x-24=0 \\ x=[?] \end{array} Remember the quadratic formula: x=b±b24ac2ax=\frac{-b \pm \sqrt{b^{2}-4 a c}}{2 a}

STEP 1

What is this asking?
We need to find the values of xx that make this specific quadratic equation equal to zero.
Watch out!
Don't forget there are two solutions to most quadratic equations, thanks to the plus-or-minus in the quadratic formula!

STEP 2

1. Identify Coefficients
2. Apply the Quadratic Formula
3. Simplify the Expression
4. Calculate the Solutions

STEP 3

Alright, let's kick things off by looking at our equation: x25x24=0x^2 - 5x - 24 = 0.
Remember, the standard form of a quadratic equation is ax2+bx+c=0ax^2 + bx + c = 0.

STEP 4

So, matching things up, we can see that our coefficients are a=1a = 1, b=5b = -5, and c=24c = -24. Crucially, don't forget that negative sign in front of the 5 and 24!

STEP 5

Now, let's bring in the star of the show: the quadratic formula itself! x=b±b24ac2ax = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}

STEP 6

Let's plug in those coefficients we just found: a=1a = 1, b=5b = -5, and c=24c = -24.
x=(5)±(5)241(24)21x = \frac{-(-5) \pm \sqrt{(-5)^2 - 4 \cdot 1 \cdot (-24)}}{2 \cdot 1}

STEP 7

Time to clean things up!
First, that double negative in front of the 5 becomes a positive 5.
x=5±(5)241(24)21x = \frac{5 \pm \sqrt{(-5)^2 - 4 \cdot 1 \cdot (-24)}}{2 \cdot 1}

STEP 8

Next, inside the square root, (5)2(-5)^2 is (5)(5)(-5) \cdot (-5), which gives us positive 25.
Then, 41(24)4 \cdot 1 \cdot (-24) gives us -96.
x=5±25(96)2x = \frac{5 \pm \sqrt{25 - (-96)}}{2}

STEP 9

Subtracting a negative is the same as adding, so 25(96)25 - (-96) becomes 25+96=12125 + 96 = 121.
x=5±1212x = \frac{5 \pm \sqrt{121}}{2}

STEP 10

The square root of 121 is 11, because 1111=12111 \cdot 11 = 121.
x=5±112x = \frac{5 \pm 11}{2}

STEP 11

Almost there!
Now we split the plus-or-minus into two separate calculations.
x=5+112orx=5112x = \frac{5 + 11}{2} \quad \text{or} \quad x = \frac{5 - 11}{2}

STEP 12

For the first one, 5+112=162=8\frac{5 + 11}{2} = \frac{16}{2} = 8.
x=8x = 8

STEP 13

For the second one, 5112=62=3\frac{5 - 11}{2} = \frac{-6}{2} = -3.
x=3x = -3

SOLUTION

So, our two solutions are x=8x = 8 and x=3x = -3!

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