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Solve by completing the square.

[tex]\[ x^2 - 14x = -40 \][/tex]

Select each correct answer.

A. [tex]\(-10\)[/tex]
B. [tex]\(-4\)[/tex]
C. 0
D. 4
E. 10


Sagot :

Certainly! Let's solve the equation [tex]\( x^2 - 14x = -40 \)[/tex] by completing the square step-by-step.

1. Start with the given equation:
[tex]\[ x^2 - 14x = -40 \][/tex]

2. First, we'll move the [tex]\( -40 \)[/tex] to the left side to set the equation to zero:
[tex]\[ x^2 - 14x + 40 = 0 \][/tex]

3. Now, let's complete the square on [tex]\( x^2 - 14x \)[/tex]. To do this, take half of the coefficient of [tex]\( x \)[/tex] (which is [tex]\(-14\)[/tex]), square it, and add and subtract this value inside the equation.

Half of [tex]\(-14\)[/tex] is:
[tex]\[ \frac{-14}{2} = -7 \][/tex]

Squaring [tex]\(-7\)[/tex] gives us:
[tex]\[ (-7)^2 = 49 \][/tex]

4. Add and subtract 49 inside the equation:
[tex]\[ x^2 - 14x + 49 - 49 + 40 = 0 \][/tex]

This can be written as:
[tex]\[ (x - 7)^2 - 9 = 0 \][/tex]

5. Isolate the perfect square term:
[tex]\[ (x - 7)^2 = 9 \][/tex]

6. Take the square root of both sides to solve for [tex]\(x\)[/tex]:
[tex]\[ x - 7 = \pm 3 \][/tex]

This gives us two solutions:
[tex]\[ x - 7 = 3 \quad \text{or} \quad x - 7 = -3 \][/tex]

7. Solve for [tex]\(x\)[/tex] in each case:
[tex]\[ x - 7 = 3 \implies x = 10 \][/tex]
[tex]\[ x - 7 = -3 \implies x = 4 \][/tex]

So, the solutions to the equation [tex]\( x^2 - 14x = -40 \)[/tex] are [tex]\( x = 4 \)[/tex] and [tex]\( x = 10 \)[/tex].

Therefore, the correct answers are:
- 4
- 10