Q. \(x^2 + 2x + 5 = 0\)

Answer

Solve \(x^2+2x+5=0\) using the quadratic formula \(x=\frac{-b\pm\sqrt{b^2-4ac}}{2a}\) with \(a=1\), \(b=2\), \(c=5\).

\[
\Delta=b^2-4ac=2^2-4(1)(5)=4-20=-16
\]
\[
x=\frac{-2\pm\sqrt{-16}}{2}=\frac{-2\pm 4i}{2}=-1\pm 2i
\]

Final answer: \(x=-1+2i\) or \(x=-1-2i\).

Detailed Explanation

We want to solve the equation

\[
x^2 + 2x + 5 = 0.
\]

Step 1: Identify the coefficients.

Compare with the standard quadratic form

\[
ax^2 + bx + c = 0.
\]

Here:

\[
a = 1,\quad b = 2,\quad c = 5.
\]

Step 2: Use the quadratic formula.

The solutions to \(ax^2 + bx + c = 0\) are given by

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

Step 3: Substitute \(a\), \(b\), and \(c\).

\[
x = \frac{-2 \pm \sqrt{2^2 – 4(1)(5)}}{2(1)}.
\]

Step 4: Simplify inside the square root (the discriminant).

Compute \(b^2 – 4ac\):

\[
2^2 – 4(1)(5) = 4 – 20 = -16.
\]

Step 5: Substitute the discriminant back in.

\[
x = \frac{-2 \pm \sqrt{-16}}{2}.
\]

Step 6: Simplify the square root of a negative number.

Since \(-16 = 16(-1)\), we have

\[
\sqrt{-16} = \sqrt{16}\sqrt{-1} = 4i,
\]

where \(i\) is the imaginary unit with \(i^2 = -1\).

Step 7: Final simplification.

\[
x = \frac{-2 \pm 4i}{2}.
\]

Split the division:

\[
x = \frac{-2}{2} \pm \frac{4i}{2}.
\]

\[
x = -1 \pm 2i.
\]

So the solutions are:

\[
\boxed{x = -1 + 2i \quad \text{and} \quad x = -1 – 2i.}
\]

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Algebra FAQ

How do I solve \(x^2+2x+5=0\) using the quadratic formula?

\(x=\frac{-b\pm\sqrt{b^2-4ac}}{2a}=\frac{-2\pm\sqrt{4-20}}{2}=-1\pm 2i\).

What is the discriminant of \(x^2+2x+5=0\)? And what does it tell me?

\(b^2-4ac=2^2-4(1)(5)=4-20=-16\). Since it’s negative, there are two complex conjugate roots.

Can I solve \(x^2+2x+5=0\) by completing the square?

\(x^2+2x+5=(x+1)^2+4=0\). So \((x+1)^2=-4\), giving \(x=-1\pm 2i\).

What are the real solutions to \(x^2+2x+5=0\)?

None. The discriminant is \(-16<0\), so there are no real roots.

Are the solutions complex numbers? What is their form?

Yes. The solutions are \(x=-1+2i\) and \(x=-1-2i\), a complex conjugate pair.

How can I verify the roots \(x=-1\pm 2i\) work in the equation?

Substitute \(x=-1+2i\): \(x^2+2x+5=(-4-4i+1+2+5)+4i=0\). Same for \(-1-2i\).
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