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.

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.

The surface area of a cube is (2 x length x width) + (2 x width x height) + (2 x length x height):

sa = 2lw + 2wh + 2lh
sa = (2 x 1 x 2) + (2 x 2 x 5) + (2 x 1 x 5)
sa = (4) + (20) + (10)
sa = 34

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

AD = AB + BD

The surface area of a cylinder is 2πr² + 2πrh:

sa = 2πr² + 2πrh
sa = 2π(3²) + 2π(3 x 9)
sa = 2π(9) + 2π(27)
sa = (2 x 9)π + (2 x 27)π
sa = 18π + 54π
sa = 72π