Q. \(x^2-5x-14=0\)

Answer

We solve the quadratic \(x^2-5x-14=0\) by factoring:

Find two numbers that multiply to \(-14\) and add to \(-5\): \(-7\) and \(2\).

\[
x^2-5x-14=(x-7)(x+2)=0
\]

So \(x-7=0\) or \(x+2=0\).

\[
x=7 \quad \text{or} \quad x=-2
\]

Final answers: \(x=7\) or \(x=-2\).

Detailed Explanation

We want to solve the quadratic equation

\[
x^{2}-5x-14=0
\]

Step 1: Factor the quadratic (if possible).

For a quadratic in the form \(ax^{2}+bx+c\), factoring works when we can write it as \((x-r)(x-s)=0\), where \(r\) and \(s\) satisfy:

\[
r+s = 5 \quad \text{and} \quad rs = -14
\]

We need two numbers whose product is \(-14\) and whose sum is \(5\).

Step 2: Find the two numbers.

The factor pairs of \(14\) are \(1\cdot 14\) and \(2\cdot 7\). To get a product of \(-14\), one number must be negative:

\[
(-1)\cdot 14 = -14 \quad \text{and} \quad (-2)\cdot 7 = -14
\]

Now check their sums:

\[
(-1)+14 = 13 \quad (\text{not } 5)
\]

\[
(-2)+7 = 5 \quad (\text{works})
\]

Step 3: Write the factored form.

Since \(r=-2\) and \(s=7\), we can factor the quadratic as:

\[
x^{2}-5x-14 = (x-7)(x+2)
\]

Step 4: Use the zero product property.

If \((x-7)(x+2)=0\), then either:

\[
x-7=0 \quad \text{or} \quad x+2=0
\]

Step 5: Solve each linear equation.

First equation:

\[
x-7=0
\]

Add \(7\) to both sides:

\[
x=7
\]

Second equation:

\[
x+2=0
\]

Subtract \(2\) from both sides:

\[
x=-2
\]

Final Answer:

\[
x=7 \quad \text{or} \quad x=-2
\]

See full solution

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Algebra FAQ

Solve \(x^2-5x-14=0\) by factoring.

Find numbers with product \(-14\) and sum \(-5\): \(-7\) and \(2\). So \((x-7)(x+2)=0\). Hence \(x=7\) or \(x=-2\).

Use the quadratic formula for \(x^2-5x-14=0\).

With \(a=1,b=-5,c=-14\): \(\Delta=b^2-4ac=25+56=81\). Then \(x=\frac{5\pm\sqrt{81}}{2}=\frac{5\pm9}{2}\), giving \(x=7,-2\).

Check the solutions \(x=7\) and \(x=-2\).

Substitute: for \(x=7\), \(49-35-14=0\). For \(x=-2\), \(4+10-14=0\). Both satisfy the equation.

What is the discriminant of \(x^2-5x-14=0\)?

\(\Delta=(-5)^2-4(1)(-14)=25+56=81\). Since \(\Delta>0\), there are two distinct real roots.

How do I know the factoring method works here?

The constant term is \(-14\) and leading coefficient is \(1\), so \((x+m)(x+n)\) is possible. We need \(m+n=-5\) and \(mn=-14\), which gives \(m=-7,n=2\).
Use this divider to practice.
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