Download (Solving Equations as Formulas).

Problems of the Day
1. 4(2a  1)  10(a  5)
2. 2( w  3)  5  3( w  1)
3. 1  2 y  3  1 y
4
4.
3
4
5 x 1

12
4
3
a=3
w=2
y = -3/2
x = 2/3
Algebra 1 ~ Chapter 3.8
Solving Equations as Formulas
Solving Formulas
• Some equations contain more than one variable.
y = mx+b,
P = a+b+c,
A = ½bh
• Remember that “solving” means to get the
variable by itself, NOT to get a numerical answer.
(x = __ )
• All rules still apply:
– Undo whatever was done to the variable you are
solving for
– Treat all other variables that you are NOT solving for
like they are numbers
How to Solve Formulas
Example - Solve the equation A = ½bh, for h.
Ask yourself:
• What is being done to h, the variable being solved for? (Turn the
car around and go home….)
• How do I undo what is being done?
A = ½bh, solve for h
2A = (½bh)2
2A = bh
b b
h=
2A
b
Solve for h means getting
h = _________
Get rid of ½ by multiplying
both sides by 2.
Get h alone by “undoing” bh.
Divide each side by b.
Example 1
Solve d = rt, for r
d=r∙t
t
t
d
r
t
Get r = ________
Undo multiplication
Example 2
Solve P = 2L + 2W, for L
-2W
-2W
P – 2W = 2L
2
2
P  2w
L
2
Get “L” by itself, L=_______
Want to get rid of the whole term
2w, so subtract 2w from both sides
of the equation.
Undo 2L by dividing both sides by
2.
Example 3
Solve ax – c = b for x.
+c +c
ax = b + c
a
a
bc
x
a
Want to get x = __
“Undo” subtraction
“Undo” multiplication
Assignment
• Skills Practice 3-8 (In-Class)
• Pages 168-169 #'s 4-12 (all), 13-25 (odds),
31-35 (all) (Homework)
• Pages 158-159 #’s 29-33 (all) (Homework)
• Quiz on Sections 3-4 to 3-6 next class!!!!