§ 2.6
Formulas
Simple Interest
Interest = principal · rate · time
Example:
Sally Simon decided to borrow $6000 from her bank
to help pay for a car. Her loan was for 3 years at a
simple interest rate of 8%. How much interest will
Sally pay?
Interest = principal · rate · time
= (6000)(0.08)(3)
= $1440
Sally will pay $1440 interest.
Angel, Elementary Algebra, 7ed
2
Geometric Formulas
The perimeter, (P) is the sum of the
lengths of the side of a figure.
The area, (A) is the total surface within the
figure’s boundaries.
A quadrilateral is the general name for a
four-sided figure.
Angel, Elementary Algebra, 7ed
3
Formulas for Quadrilaterals and Triangles
Figure
Sketch
Square
s
Rectangle
w
Area
Perimeter
A = s2
P = 4s
A = lw
P = 2l + 2w
A = lh
P = 2l + 2w
A=
h(b+d)
P = a+b+c+d
A = bh
P = a+b+c
l
h
Parallelogram
w
l
Trapezoid
a
b
h
d
Triangle
a
hc
b
c
Angel, Elementary Algebra, 7ed
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Geometric Formulas
Example:
Mike Morgan has a rectangular lot that measures 100
feet by 60 feet. If Mike wants to fence in his lot, how
much fencing will he need? What is the area of the lot?
P = 2(100) + 2(60) = 200 + 120 = 320 ft
A = lw = 100(60) = 6000 feet2
Angel, Elementary Algebra, 7ed
5
Geometric Formulas
The circumference, (C) is the
distance around a circle.
The radius, (r) is the line segment from
the center of the circle to any point on
the circle.
The diameter of a circle is a line
segment through the center whose
endpoints both lie on the circle.
Angel, Elementary Algebra, 7ed
C
r
d
6
Geometric Formulas
Formulas for Circles
Circle
Area
Circumference
r
A =  r2
C = 2 r
The value of pi, () is an irrational number.
Pi is approximately equal to 3.14.
Angel, Elementary Algebra, 7ed
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Geometric Formulas
Example:
A circular swimming pool has a diameter of 24
feet. What is the circumference of the pool?
Remember that the radius is half of the diameter.
C = 2 r = 2 (3.14)(12)  75.4
The circumference is approximately 75.4 feet.
Angel, Elementary Algebra, 7ed
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Formulas for Quadrilaterals and Triangles
Figure
Rectangular Solid
Sketch
V = lwh
h
w
l
Right Circular
Cylinder
Right Circular
Cone
Sphere
Volume
h r
h
r
r
Angel, Elementary Algebra, 7ed
V =  r2h
V =  r2h
V =  r3
9
Geometric Formulas
Volume is measured in cubic units, such as cubic
inches or cubic meters.
Example:
Bob has an empty oil drum that he uses for
storage. The drum is 4 feet high and has a
diameter of 24 inches. Find the volume of
the drum. (Hint: 24 inches = ? feet)
V =  r2h = 3.14(1)2(4)  12.56 ft3
Angel, Elementary Algebra, 7ed
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