To solve this, use the Pythagorean Theorem: a² + b² = c² where a and b are legs (sides) and c is the hypotenuse (in this case z or the missing side). So, your new equation is: 15² + 18² = z² or 225 + 324 = z². Add 225 + 324 to get 549. To solve for z, find the square root of 549: 23.430749. Rounded to the nearest tenth, this is 23.4.
