A right angle measures 90 degrees and is the intersection of two perpendicular lines. In diagrams, a right angle is indicated by a small box completing a square with the perpendicular lines.

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 d° = 164, the value of b° is 164.

To combine like terms, add or subtract the coefficients (the numbers that come before the variables) of terms that have the same variable raised to the same exponent.

5a⁵ + 8a⁵ = 13a⁵

To solve this equation, repeatedly do the same thing to both sides of the equation until the variable is isolated on one side of the < sign and the answer on the other.

8x + 8 < \( \frac{x}{1} \)
1 x (8x + 8) < x
(1 x 8x) + (1 x 8) < x
8x + 8 < x
8x + 8 - x < 0
8x - x < -8
7x < -8
x < \( \frac{-8}{7} \)
x < -1\(\frac{1}{7}\)

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