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° = 13, the value of a° is 13.

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

a = ½bh
a = ½ x 5 x 5 = \( \frac{25}{2} \) = 12\(\frac{1}{2}\)

The perimeter of a triangle is the sum of the lengths of its sides:

p = x + y + z
p = 8cm + 11cm + 13cm = 32cm

A rhombus is a parallelogram with four equal-length sides. A square is a rectangle with four equal-length sides.

A line on the coordinate grid can be defined by a slope-intercept equation: y = mx + b. For a given value of x, the value of y can be determined given the slope (m) and y-intercept (b) of the line. The slope of a line is change in y over change in x, \({\Delta y \over \Delta x}\), and the y-intercept is the y-coordinate where the line crosses the vertical y-axis.