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).

The entire length of this line is represented by AD which is AB + BD:

AD = AB + BD

The area of a triangle is equal to ½ base x height:

a = ½bh
a = ½ x 1 x 4 = \( \frac{4}{2} \) = 2

To factor a quadratic expression, apply the FOIL method (First, Outside, Inside, Last) in reverse. First, find the two Last terms that will multiply to produce 16 as well and sum (Inside, Outside) to equal -10. For this problem, those two numbers are -8 and -2. Then, plug these into a set of binomials using the square root of the First variable (y²):

y² - 10y + 16
y² + (-8 - 2)y + (-8 x -2)
(y - 8)(y - 2)

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 z° = 39, the value of c° is 39.