Find the length of all three sides of one triangle. As an example, assume the sides of triangle A have the following lengths: side "a" is 4 inches, side "b" 6 inches and side "c" is 8 inches.
Find the length of one side of a similar triangle. As an example, assume you have only side "a" of triangle B which is a similar triangle to triangle A. Assume side "a" of triangle B is 6 inches. Note, side "a" in triangle A and side "a" in triangle B are referred to as corresponding sides.
Find the ratio using the known corresponding sides according to the following formula: ratio = (known corresponding side of first triangle)/(known corresponding side of second triangle). Using the example, ratio = side a of triangle A/side a of triangle B. In the example, the ratio is 4/6, or 2/3.
Calculate the unknown sides using the ratio. Side b of Triangle B = (Side b of triangle A) x (ratio). Using the example, (6) x (2/3) = 4 inches. Side c of Triangle B = (Side c of triangle A) x (ratio). Using the example, (8) x (2/3) = 5.33 inches.