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Geometry Formulas
When a problem involves geometry, it is often very helpful to draw a picture.
You will need to know these formulas for problems on homework and tests.
1. Area:
Rectangle
Parallelogram:
Triangle:
h
h
l
b
w
A = lw
Square:
h
s
b2
s
b
A = bh
Trapezoid:
b1
A = ½ b·h
A = s2
A =½ (b1+ b2)h
2. Perimeter of any Figure: To find the perimeter of a figure, add the lengths of all the sides.
Rectangle:
Triangle:
a
l
w
Square:
b
s
s
c
P = 2l +2w
P=a+b+c
P = 4s
3. Volume: The volume of a rectangular solid is: V = lwh
4. Angles:
h
The sum of the angles in a triangle is 180°.
w
l
The sum of the angles in a quadrilateral is 360°.
(A quadrilateral is any four sided figure, including rectangles.)
Complementary angles sum to 90°.
If an angle measures x degrees, its complement measures 90 – x degrees.
Supplementary angles sum to 180°.
If an angle measures x degrees, its supplement measures 180 – x degrees.
5. Circles:
Area:
Circumference:
(distance around)
A = C = 2
3.14
r
or 6. Sides of a Right Triangle: (not for this chapter)
The relationship between the sides of a right triangle
(where c is the hypotenuse or longest side) is:
a2 + b2 = c2
c
a
b