The first step to solve a quadratic equation that's set to zero is to factor the quadratic equation:

a² + 7a - 18 = 0
(a - 2)(a + 9) = 0

For this expression to be true, the left side of the expression must equal zero. Therefore, either (a - 2) or (a + 9) must equal zero:

If (a - 2) = 0, a must equal 2
If (a + 9) = 0, a must equal -9

So the solution is that a = 2 or -9

The formula for area is πr². Radius is circle \( \frac{diameter}{2} \):

r = \( \frac{d}{2} \)
r = \( \frac{4}{2} \)
r = 2
a = πr²
a = π(2²)
a = 4π

A circle is a figure in which each point around its perimeter is an equal distance from the center. The radius of a circle is the distance between the center and any point along its perimeter. A chord is a line segment that connects any two points along its perimeter. The diameter of a circle is the length of a chord that passes through the center of the circle and equals twice the circle's radius (2r).

To factor a quadratic expression, apply the FOIL (First, Outside, Inside, Last) method in reverse.

For parallel lines with a transversal, the following relationships apply:

• angles in the same position on different parallel lines equal each other (a° = w°, b° = x°, c° = z°, d° = y°)
• alternate interior angles are equal (a° = z°, b° = y°, c° = w°, d° = x°)
• all acute angles (a° = c° = w° = z°) and all obtuse angles (b° = d° = x° = y°) equal each other
• same-side interior angles are supplementary and add up to 180° (e.g. a° + d° = 180°, d° + c° = 180°)

Applying these relationships starting with a° = 25, the value of c° is 25.