Consider the following equations. Solve them by showing your work clearly and step by step. Show a proof

1. 7x² + 23x = 60
2. x(x - 5)(x - 2) = 4
3. (x - 3)² = 0

1 answer

Let's solve each equation step by step.

1. Solve the equation: \(7x^2 + 23x = 60\)

Step 1: Rearrange the equation to standard quadratic form.

Subtract 60 from both sides:

\[ 7x^2 + 23x - 60 = 0 \]

Step 2: Apply the quadratic formula.

The quadratic formula is:

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

For our equation \(7x^2 + 23x - 60 = 0\), the coefficients are:

  • \(a = 7\)
  • \(b = 23\)
  • \(c = -60\)

Step 3: Calculate the discriminant (\(b^2 - 4ac\)).

\[ b^2 - 4ac = 23^2 - 4 \cdot 7 \cdot (-60) = 529 + 1680 = 2209 \]

Step 4: Calculate the roots.

\[ x = \frac{-23 \pm \sqrt{2209}}{2 \cdot 7} = \frac{-23 \pm 47}{14} \]

Now calculate two solutions:

  1. \(x = \frac{-23 + 47}{14} = \frac{24}{14} = \frac{12}{7}\)
  2. \(x = \frac{-23 - 47}{14} = \frac{-70}{14} = -5\)

Final Solutions:

\[ x = \frac{12}{7} \quad \text{and} \quad x = -5 \]


2. Solve the equation: \(x(x - 5)(x - 2) = 4\)

Step 1: Expand the left side.

First, expand \(x(x - 5)(x - 2)\):

  1. Expand \((x - 5)(x - 2)\):

\[ (x - 5)(x - 2) = x^2 - 2x - 5x + 10 = x^2 - 7x + 10 \]

  1. Multiply by \(x\):

\[ x(x^2 - 7x + 10) = x^3 - 7x^2 + 10x \]

Now we rewrite the equation:

\[ x^3 - 7x^2 + 10x = 4 \]

Step 2: Rearrange to standard form.

Subtract 4 from both sides:

\[ x^3 - 7x^2 + 10x - 4 = 0 \]

Step 3: Use the Rational Root Theorem.

Let's test rational roots like \(x = 1\):

\[ 1^3 - 7(1^2) + 10(1) - 4 = 1 - 7 + 10 - 4 = 0 \]

So, \(x = 1\) is a root. We can perform synthetic division to factor the cubic polynomial.

Step 4: Factor out \((x - 1)\).

Perform synthetic division of \(x^3 - 7x^2 + 10x - 4\) by \(x - 1\):

1 | 1 | -7 | 10 | -4 --|---|----|---|--- | | 1 | -6 | 4 | 1 | -6 | 4 | 0

The result is:

\[ x^2 - 6x + 4 \]

Step 5: Solve \(x^2 - 6x + 4 = 0\) using the quadratic formula.

\[ x = \frac{6 \pm \sqrt{(-6)^2 - 4 \cdot 1 \cdot 4}}{2 \cdot 1} = \frac{6 \pm \sqrt{36 - 16}}{2} = \frac{6 \pm \sqrt{20}}{2} = \frac{6 \pm 2\sqrt{5}}{2} = 3 \pm \sqrt{5} \]

Final Solutions:

\[ x = 1, \quad x = 3 + \sqrt{5}, \quad x = 3 - \sqrt{5} \]


3. Solve the equation: \((x - 3)^2 = 0\)

Step 1: Take the square root.

Taking the square root on both sides:

\[ x - 3 = 0 \]

Step 2: Solve for \(x\).

Add 3 to both sides:

\[ x = 3 \]

Final Solution:

\[ x = 3 \]


Summary of Solutions

  1. \(x = \frac{12}{7}\) and \(x = -5\)
  2. \(x = 1\), \(x = 3 + \sqrt{5}\), \(x = 3 - \sqrt{5}\)
  3. \(x = 3\)