Transcript Zero and Negative Exponents

Zero and Negative Exponents
Section 7-1
Goals
Goal
• To simplify expressions
involving zero and negative
exponents.
Rubric
Level 1 – Know the goals.
Level 2 – Fully understand the
goals.
Level 3 – Use the goals to
solve simple problems.
Level 4 – Use the goals to
solve more advanced problems.
Level 5 – Adapts and applies
the goals to different and more
complex problems.
Vocabulary
• None
Reciprocals
• When working with negative exponents you need to
know what a reciprocal is…
• We already covered this earlier in the course so as a
quick review…
• A reciprocal is a fraction that is inverted and the
product is 1. It looks like this:
Example:
Original
2
6
Reciprocal
●
6
2
Product
=
1
Zero and Negative Exponents
You have seen positive exponents. Recall that to simplify
32, use 3 as a factor 2 times: 32 = 3  3 = 9.
But what does it mean for an exponent to be negative or 0?
You can use a table and look for a pattern to figure it out.
54
53
Power 55
Value 3125 625 125
5
5
5
52
51
50
5–1
5–2
25
5
1
1/5
1/25
5
When the exponent decreases by one, the value of the power is divided by
5. Continue the pattern of dividing by 5.
Remember!
Base
4
x
Exponent
Definition
DEFINITION OF ZERO EXPONENTS
a0 = 1 ,
A nonzero number to the zero power has the
value of ONE. ANY NUMBER (except zero!) RAISED TO THE
ZERO POWER IS ONE!!!!
a0 = 1, where a is not equal to 0.
-40 = 1
50
-90 = 1
1,5670
=1
7650
1000 = 1
=1
=1
19870 = 1
970 = 1
80 = 1
3000
1,000,0000
=1
-220 = 1
=1
22.8790 = 1
Zero Exponents
• Why is 00 undefined?
• The property of zero as an exponent implies the
following pattern.
?
0
0
0
0
3 =1 2 =1 1 =1 0 =1
• However, switching the exponent and the base
implies the following pattern.
?
3
2
1
0
0 =0 0 =0 0 =0 0 =0
• It is not possible for 00 to equal both 1 and 0. So,
00 is undefined.
Definition
DEFINITION OF NEGATIVE EXPONENTS
a
n
1
 n , where a is not equal to 0.
a
a-n is the reciprocal of an
What this really means is that you turn a negative exponent
into a positive exponent by shifting the power from
numerator to denominator or vice versa!
Reading Math
2–4 is read “2 to the negative fourth power.”
Negative Exponents
What this really means is that you turn a negative
exponent into a positive exponent by shifting the power
from numerator to denominator or vice versa!
1 1
2  2 
2
4
2
1
1
4  3 
4
64
3
Important – only move the base number and the negative exponent
that goes with it!
Negative Exponents
• Why is an expression with a base of 0 and a
negative exponent undefined?
• Using 0 as a base with a negative exponent
will result in division by zero, which is
undefined.
1 1

2
0   undefined
02 0
Negative Exponents
• What does 2-1 Mean?
• You cannot leave an exponent negative because
there is no way to express it’s meaning.
• You must make it positive!
1
2  1
2
1
An algebraic expression is in simplest form when powers with a
variable base are written with only positive exponents.
Example: Application
One cup is 2–4 gallons. Simplify this expression.
cup is equal to
Your Turn:
A sand fly may have a wingspan up to 5–3 m. Simplify this
expression.
5-3 m is equal to
Example: Zero & Negative
Exponents
Simplify.
A. 4–3
B. 70
7º = 1
C. (–5)–4
D. –5–4
Any nonzero number raised to the zero power is 1.
Caution
In (–3)–4, the base is negative because the negative
sign is inside the parentheses. In –3–4 the base (3) is
positive.
Your Turn:
Simplify.
a. 10–4
b. (–2)–4
c. (–2)–5
d. –2–5
Example:
Evaluate the expression for the given value of the variables.
x–2 for x = 4
Substitute 4 for x.
Use the definition
Example:
Evaluate the expression for the given values of the variables.
–2a0b-4 for a = 5 and b = –3
Substitute 5 for a and –3 for b.
Evaluate expressions with exponents.
Write the power in the denominator
as a product.
Evaluate the powers in the
product.
Simplify.
Your Turn:
Evaluate the expression for the given value of the variable.
p–3 for p = 4
Substitute 4 for p.
Evaluate exponent.
Write the power in the denominator
as a product.
Evaluate the powers in the
product.
Your Turn:
Evaluate the expression for the given values of the variables.
for a = –2 and b = 6
Substitute –2 for a and 6 for b.
Evaluate expressions with exponents.
Write the power in the denominator
as a product.
Evaluate the powers in the
product.
2
Simplify.
More Negative Exponents
What if you have an expression with a negative
exponent in a denominator, such as
or
?
Definition of a negative exponent.
Substitute –8 for n.
Simplify the exponent on the right
side.
So if a base with a negative exponent is in a denominator, it is equivalent to the same base
with the opposite (positive) exponent in the numerator.
An expression that contains negative or zero exponents is not considered to be
simplified. Expressions should be rewritten with only positive exponents.
Example:
Simplify.
A. 7w–4
B.
Example:
Simplify.
C.
and
Your Turn:
Simplify.
a. 2r0m–3
rº = 1 and
b.
c.
.
Review
Joke Time
• What washes up on tiny beaches?
• Microwaves!
• What’s the best way to crave wood?
• Whittle by whittle!
• What do you do when you see a spaceman?
• Park your car, man.
Assignment
• 7-1 Exercises Pg. 444 - 446: #10 – 54 even,
60 – 66 even.