GED Math: Geometry Formulas You Should Review
Geometry is an important topic to include in your GED Mathematical Reasoning preparation. Questions may involve shapes, measurements, perimeter, area, or volume. Understanding what each formula calculates is just as important as remembering the formula itself. Practice identifying the shape, selecting the correct formula, and checking that your answer uses the right units.
1. Perimeter of a Rectangle
Perimeter is the total distance around a two-dimensional shape. For a rectangle, the formula is: P=2l+2w Here, l represents length and w represents width. Suppose a rectangle has a length of 8 centimeters and a width of 3 centimeters. P=2(8)+2(3)=22 The perimeter is 22 centimeters. Remember that perimeter is measured in ordinary length units, such as centimeters or meters.
2. Area of a Rectangle
Area measures the amount of space inside a two-dimensional shape. The formula for a rectangle is: A=l×w If a rectangle is 8 centimeters long and 3 centimeters wide: A=8×3=24 The area is 24 square centimeters. Notice that the units are squared because area measures a two-dimensional space.
3. Area of a Triangle
The area of a triangle is: A= 2 1 bh Here, b is the base and h is the perpendicular height. Suppose a triangle has a base of 10 meters and a height of 6 meters. A= 2 1 (10)(6)=30 The area is 30 square meters. Be careful to use the perpendicular height rather than a sloping side unless the problem gives enough information to determine the height.
4. Circumference of a Circle
Circumference is the distance around a circle. The formula is: C=2πr Here, r represents the radius, which is the distance from the center of the circle to its edge. If a circle has a radius of 4 centimeters: C=2π(4)=8π Using π≈3.14, the circumference is approximately 25.12 centimeters. If a question gives the diameter instead, remember that the diameter is twice the radius.
5. Area of a Circle
The formula for the area of a circle is: A=πr 2 For a circle with a radius of 4 centimeters: A=π(4 2 )=16π Using 3.14 for π, the area is approximately 50.24 square centimeters. Remember to square the radius before multiplying by π.
6. Volume of a Rectangular Prism
Volume measures the amount of space inside a three-dimensional object. For a rectangular prism: V=lwh Suppose a box has a length of 5 centimeters, a width of 3 centimeters, and a height of 2 centimeters. V=5×3×2=30 The volume is 30 cubic centimeters.
How to Remember Geometry Formulas
Group formulas by what they calculate: Measurement Example formula Rectangle perimeter P=2l+2w Rectangle area A=lw Triangle area A= 2 1 bh Circle circumference C=2πr Circle area A=πr 2 Rectangular prism volume V=lwh Practice identifying the shape and the measurement being requested before selecting a formula.
Final Thoughts
Geometry becomes easier when you connect each formula to the shape and measurement it represents. Practice with diagrams and word problems, and always check whether the question asks for perimeter, area, or volume.
