Formulas
Chapter 2, Section 2
 Formulas
 A formula is a general representation of an equation (or relationship).
 A formula will have many variables and few specific numbers in it.

is a formula for speed where v is the speed, d is the distance, and t is the time.
 Evaluating Formulas
 Given: the formula.
 Given: values for all but one variable.
 Goal: determine the value of the unknown variable for the given variable values.

when d = 300 miles and t = 5 hours.

Answer: v = 
300 miles 5 hours 
= 60 mph. 
 Solving for One Variable of a Formula
 Given: the formula.
 Asked to: solve for a particular variable.
 Goal: isolate the particular variable on the left hand side with everything else on the right hand side.

solve for t.

 Subscripts
 Subscripts are smaller numbers or letters placed to the lower right of letters.
 Formulas often contain variables with subscripts.

 Examples
 x_{1} is read "x sub 1" and 1 is the subscript.
 R_{k} is read "R sub k" and k is the subscript.
 Some Greek Letters (and Common Meanings)
 Greek letters are often used in formulas.
 Some greek letters have meanings that are usually associated with them.

Letter

Meaning

(small pi) 
a constant (see to 1000 places) 
(small theta) 
an angle 
(capital sigma) 
summation of many 
(capital pi) 
product of many 
 Some Common Formulas

Formula

Use

A = r^{2} 
Area of a circle. r is the radius 
C = 2r 
Circumference of a circle. r is the radius 
A = LW 
Area of a rectangle. L is length, W is width 
P = 2L + 2W 
Perimeter of a rectangle. L is length, W is width 

Area of a triangle. B is base length, H is height 
a^{2} + b^{2} = c^{2} 
Pythagoean theorem for a right triangle. a, b lengths of legs
c length of hypotenuse 
A = Prt 
Simple interest. A is interest earned, P is the principal, r is the interest rate (decimal), t is time 

Compound interest. A is interest earned, P is principal, r is interest rate (decimal),
n is number of times interest is paid per year,
t is time in years 
A = Rt 
Rates. A is amount, R is rate, t is time 
d = vt 
Distance and speed. d is distance, v is speed, t is time 

Temperature conversion. F is degrees Fahrenheit
C is degrees Centigrade 
