Basic Geometry Formulas - Area, Perimeter, Volume If a square has an area of 49 ft2, what is the length of one of its sides? The perimeter? If a rectangle has a width of 4, how long must its length be so that the area is 36? If one angle of a right triangle is 70 degree, what are the other 2 angles. What is the diameter of a circle with an area of 16 π ?