Rewrite Equations and Formulas

Lesson 3.8

OBJ: To recognize and solve literal equations; to rewrite equations and formulas.

Literal Equation

 An equation with two or more variables.

 An equation in which letters are used to replace coefficients and constants of another equation.  Examples:

A

 

r

2

x

1

x

2

ax

 

b

3  

c

0

P

 2

l

 2

w

Solving Literal Equations

 Solving equations for one variable in terms of the other variables without substituting any values.

 Examples:  Solve V =lwh for h.  Solve A = p +prt for r.  Solve A = p + prt for p.

**Use the same rules for solving equations. The only difference is that it is not numbers, it is only variables.

Solve literal equations

 Solve ax + b = c for x. Then use the solution to solve 2x + 5 = 11  Step 1: Solve ax + b = c for x  Step 2: Use the solution to solve 2x + 5 = 11.

 The solution of 2x + 5 = 11 is 3.  Example: Solve p + qx = r for x. Then use the solution to solve 3+5x = -7.

Two or more variables…

 Write -2x + 3y = 6 so that y is a function of x.  This means solve for y.  Write 12 = 9x + 3y so that y is a function of x.  Write 14 = 7y – 6x so that y is a function of x.

Solve and use Geometric Formulas  The area for a rectangle is given by the formulas A = lw, where l is the length and w is the width.  Solve the formula for the length l.

 Use the rewritten formula to find the length of this rectangle. A = 351 cm 2 13 cm

Homework

 Text p. 187- 188  #’s 3-6, 12 – 18 evens, 20 -22, 24, 26, 27, 32, 33