section 1-5 subtracting real numbers spi 12c: add and subtract algebraic expressions. objectives:...
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Section 1-5 Subtracting Real NumbersSPI 12C: Add and subtract algebraic expressions.
Objectives:• Subtract real numbers using models and rules
A runner starts out running at a distance of 20 miles from her house. She runs in the direction of her house for 30 miles. How many miles did she run past her house?
-20 -10 0 10 20
Modeling Subtraction of Real Numbers
1. Model using number lines2. Model using Algebra Tiles3. Model using Matrices
Subtract –3 – 2 using a number line.
Start at –3.
Move left 2 units
Subtract Integers using a Number Line
4. Model using numbers and operation symbols
Subtract 4 – (–2) using tiles.
There are 6 positive tiles left.
Start with 4 positive tiles.
Add zero pairs until there are 2 negative tiles.
Remove 2 negative tiles.
Subtract Integers using Algebra Tiles
-3 - 5 7 - 10
Subtract Integers using Matrices
5 12–3 7
4 6 5 10
–
1 6–8 –3
=
Subtract the two matrices. Remember to subtract the
numbers in corresponding positions and place answers in
a new matrix in corresponding positions.
5 – 4 12 - 6
=
Simplify –11.6 – (–14).
–11.6 – (–14) = –11.6 + 14 The opposite of –14 is 14.
= 2.4 Add.
Subtract Integers using Numbers and Operations Symbols
Simplify |–13 – (–21)|.
|–13 – (–21)| = | –13 + 21| The opposite of –21 is 21.
= | 8 | Add within absolute value symbols.
= 8 Find the absolute value.
Rule for Subtracting NumbersTo subtract a number, add its opposite.
Examples: 3 – 5 = 3 + (-5) = -2 3 – (- 5) = 3 + 5 = 8
The temperature in Montreal, Canada,
at 6:00 P.M. was –8°C. Find the
temperature at 10:00 P.M. if it fell 7°C.
Find the temperature at 10:00 P.M. by subtracting 7°C from the temperature at 6:00 P.M.
–8 – 7 = –8 + (–7) Add the opposite.
= –15 Simplify.The temperature at 10:00 P.M. was –15°C.
Real-world example
Evaluate x – (–y) for x = –3 and y = –6.x – (–y) = –3 – [–(–6)] Substitute –3 for x and –6 for y.
= –3 – 6 The opposite of –6 is 6.
= –9 Subtract.
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