Use the Pythagorean theorem for right triangles: (a^2 + b^2 = c^2)
Identify the known sides and the missing side
Substitute the known values into the formula
Solve for the unknown side by isolating it
Take the square root if the missing side is squared
Use the Law of Sines if you know an angle and its opposite side
Use the Law of Cosines if you know two sides and the included angle
Use triangle angle sum: (A + B + C = 180^circ)
Use special triangle ratios for 30-60-90 triangles
Use special triangle ratios for 45-45-90 triangles
Check that the side lengths satisfy the triangle inequality
Verify the result matches the type of triangle given