Q. \(x^2+6x-16=0\)

Answer

We solve the quadratic equation \(x^2+6x-16=0\) by factoring. Find numbers that multiply to \(-16\) and add to \(6\): \(8\) and \(-2\). So

\[
x^2+6x-16=(x+8)(x-2)=0
\]

Set each factor equal to zero:

\[
x+8=0 \Rightarrow x=-8,\quad x-2=0 \Rightarrow x=2
\]

Final result: \(x=-8\) or \(x=2\).

Detailed Explanation

We want to solve the quadratic equation

\[
x^{2}+6x-16=0
\]

Step 1: Identify the values of \(a\), \(b\), and \(c\).

A quadratic equation in standard form looks like

\[
ax^{2}+bx+c=0
\]

Here:

  • \(a=1\)
  • \(b=6\)
  • \(c=-16\)

Step 2: Use the quadratic formula.

The quadratic formula is

\[
x=\frac{-b\pm\sqrt{b^{2}-4ac}}{2a}
\]

Substitute \(a=1\), \(b=6\), and \(c=-16\):

\[
x=\frac{-6\pm\sqrt{6^{2}-4\cdot 1\cdot (-16)}}{2\cdot 1}
\]

Step 3: Simplify inside the square root (the discriminant).

First compute \(6^{2}\):

\[
6^{2}=36
\]

Now compute \(-4ac\):

\[
-4\cdot 1\cdot (-16)=64
\]

So the discriminant is:

\[
b^{2}-4ac=36+64=100
\]

Step 4: Take the square root.

\[
\sqrt{100}=10
\]

Step 5: Substitute back into the quadratic formula.

\[
x=\frac{-6\pm 10}{2}
\]

Step 6: Split into two solutions.

First solution using \(+\):

\[
x=\frac{-6+10}{2}=\frac{4}{2}=2
\]

Second solution using \(-\):

\[
x=\frac{-6-10}{2}=\frac{-16}{2}=-8
\]

Final Answer:

\[
x=2 \quad \text{or} \quad x=-8
\]

See full solution

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Algebra FAQ

How do I factor \(x^2+6x-16=0\)?

Find numbers with sum \(6\) and product \(-16\): \(8\) and \(-2\). So \(x^2+6x-16=(x+8)(x-2)\).

What are the solutions using factoring?

Set \((x+8)(x-2)=0\). Then \(x+8=0\Rightarrow x=-8\) or \(x-2=0\Rightarrow x=2\).

How do I use the quadratic formula?

For \(ax^2+bx+c=0\), \(\displaystyle x=\frac{-b\pm\sqrt{b^2-4ac}}{2a}\). Here \(a=1\), \(b=6\), \(c=-16\): \(\displaystyle x=\frac{-6\pm\sqrt{36+64}}{2}=\frac{-6\pm10}{2}\Rightarrow x=2,-8\).

What is the discriminant and what does it tell me?

\(\Delta=b^2-4ac=36-4(1)(-16)=100\). Since \(\Delta>0\), there are two real solutions.

Can I solve by completing the square?

\(x^2+6x-16=0\Rightarrow x^2+6x=16\). Complete square: \((x+3)^2-9=16\Rightarrow (x+3)^2=25\Rightarrow x=-3\pm5\), so \(x=2,-8\).

Quick check: do \(x=2\) and \(x=-8\) satisfy the equation?

Substitute \(x=2\): \(4+12-16=0\). Substitute \(x=-8\): \(64-48-16=0\). Both work.
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