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Lesson 7~30 minUnit 2 · Patterns & Algebra+90 XP

Dividing Algebraic Terms

Division is multiplication's undo button. Learn to divide coefficients, cancel variables, and simplify algebraic fractions.

Today's hook: $8x \div 2x$. Is it $4$? Is it $4x$? Or something else? Think about what $2x$ means, then figure out what dividing by it does.
0/5QUESTS
Think First
warm-up

Simplify $\frac{8x}{2x}$. Explain what happens to the numbers and what happens to the letters.

Record in workbook.
1
The Big Idea
+5 XP to read

To divide algebraic terms: divide the coefficients, and cancel or subtract powers for the variables. It's the opposite of multiplication.

$\frac{8x}{2x}$: coefficients $8 \div 2 = 4$, variables $\frac{x}{x} = 1$. So $4 \times 1 =$ $4$. The $x$ cancels out!

$8x$ $2x$ $8 \div 2 = 4$ $x \div x = 1$ $= 4$
$\frac{8x}{2x} = \frac{8}{2} \times \frac{x}{x} = 4 \times 1 = 4$
Divide coefficients
$\frac{12}{3} = 4$. Same as normal division.
Cancel same variables
$\frac{x}{x} = 1$. They disappear! Same for $\frac{a^2}{a} = a$.
Subtract powers
$\frac{x^5}{x^2} = x^{5-2} = x^3$. Same base: subtract exponents.
2
What You'll Master
objectives

Know

  • Divide coefficients separately
  • Cancel matching variables
  • Subtract powers for same base

Understand

  • Why $\frac{x}{x} = 1$ not $0$
  • That division undoes multiplication
  • How to handle leftover variables

Can Do

  • Divide simple algebraic terms
  • Simplify algebraic fractions
  • Handle negative coefficients
3
Words You Need
vocabulary
QuotientThe result of division. $\frac{12x}{3} = 4x$.
CancelRemove matching factors from top and bottom. $\frac{3x}{3} = x$.
Algebraic FractionA fraction with algebraic terms. $\frac{6x^2}{2x} = 3x$.
SimplifyMake the fraction as short as possible.
Power Rule$\frac{x^m}{x^n} = x^{m-n}$. Subtract exponents for same base.
Top-heavyWhen the numerator has a higher power. $\frac{x^5}{x^2} = x^3$.
4
Spot the Trap
heads-up

Wrong: $\frac{6x}{2} = 3x$ is correct, but $\frac{6x}{2x} = 3x$ is NOT.

Right: $\frac{6x}{2x} = 3$. The $x$ cancels, leaving just 3.

Wrong: $\frac{x^5}{x^2} = x^{5 \div 2} = x^{2.5}$

Right: $\frac{x^5}{x^2} = x^{5-2} = x^3$. Subtract, don't divide!

5
The Power Rule
+5 XP

When dividing same variables, subtract the powers. $\frac{x^m}{x^n} = x^{m-n}$.

$\frac{x^7}{x^4}$ 7 factors on top, 4 on bottom $= x^{7-4} = x^3$ $\frac{12x^5}{3x^2}$ Coeffs: $12 \div 3 = 4$. $x$: $5-2 = 3$ $= 4x^3$
6
Dividing with Coefficients and Multiple Variables
+5 XP

Divide coefficients. Cancel each variable separately.

ExpressionCoefficientsVariablesResult
$\frac{15x^3y}{3xy}$$15 \div 3 = 5$$x^{3-1} = x^2$, $y^{1-1} = 1$$5x^2$
$\frac{-8a^2b^3}{2ab^2}$$-8 \div 2 = -4$$a^{2-1} = a$, $b^{3-2} = b$$-4ab$
$\frac{6x^2y}{3x^2}$$6 \div 3 = 2$$x^{2-2} = 1$, $y$ stays$2y$
7
When Variables Cancel Completely
+5 XP

If a variable has the same power on top and bottom, it becomes 1 and disappears.

$\frac{10x^2y^3}{5x^2y} = \frac{10}{5} \times \frac{x^2}{x^2} \times \frac{y^3}{y} = 2 \times 1 \times y^2 = 2y^2$ $x^2$ cancels! $y^3 \div y = y^2$. Coefficient: $10 \div 5 = 2$.
Try It: $\frac{18a^3b^2}{6a^2b^2}$.Ans: $3a$
8
Quick Reference Table
+5 XP
DivisionWorkingAnswer
$\frac{12x}{3}$$12 \div 3 = 4$, $x$ stays$4x$
$\frac{9x^2}{3x}$$9 \div 3 = 3$, $x^{2-1}$$3x$
$\frac{-15a^3}{5a}$$-15 \div 5 = -3$, $a^{3-1}$$-3a^2$
$\frac{8x^2y}{2xy}$$8 \div 2 = 4$, $x^{2-1}$, $y^{1-1}=1$$4x$
Watch Me Solve It · Complex division
+15 XP per step
Q
PROBLEM
Simplify $\frac{-20x^3y^2}{4x^2y}$.
  1. 1
    Divide the coefficients
    $-20 \div 4 = -5$
    Negative divided by positive gives negative. $20 \div 4 = 5$, so answer is $-5$.
  2. 2
    Divide the $x$ variables
    $\frac{x^3}{x^2} = x^{3-2} = x^1 = x$
    Subtract powers: $3 - 2 = 1$. $x^1$ is just $x$.
  3. 3
    Divide the $y$ variables
    $\frac{y^2}{y} = y^{2-1} = y^1 = y$
    $y = y^1$. Subtract: $2 - 1 = 1$. Just $y$ remains.
  4. 4
    Combine all parts
    $-5 \times x \times y = -5xy$
    Coefficient $-5$, $x$-part $x$, $y$-part $y$. Write together: $-5xy$.
Answer$-5xy$
9
Common Pitfalls
heads-up
$\frac{x^5}{x^2} = x^{5 \div 2} = x^{2.5}$
You SUBTRACT powers, not divide them!
Fix: $\frac{x^m}{x^n} = x^{m-n}$. So $\frac{x^5}{x^2} = x^{5-2} = x^3$.
$\frac{6x}{2x} = 3x$
The $x$ cancels completely! $\frac{x}{x} = 1$.
Fix: $\frac{6x}{2x} = \frac{6}{2} \times \frac{x}{x} = 3 \times 1 = 3$.
$\frac{8}{2x} = 4x$
The $x$ is ONLY in the denominator. It stays there!
Fix: $\frac{8}{2x} = \frac{4}{x}$. Only the 8 and 2 divide.

How are you completing this lesson?

D
Brain Trainer · Mixed
4 problems
  1. 1 Simplify $\frac{12x}{3}$.

    $12 \div 3 = 4$, $x$ stays. $4x$$4x$
  2. 2 Simplify $\frac{15x^3}{5x}$.

    $15 \div 5 = 3$, $x^{3-1} = x^2$. $3x^2$$3x^2$
  3. 3 Simplify $\frac{8x^2y}{2xy}$.

    $8 \div 2 = 4$, $x^{2-1} = x$, $y^{1-1} = 1$. $4x$$4x$
  4. 4 Simplify $\frac{-18a^4b^2}{3a^2b}$.

    $-18 \div 3 = -6$, $a^{4-2} = a^2$, $b^{2-1} = b$. $-6a^2b$$-6a^2b$
Complete in workbook.
1
Multiple Choice
+10 XP
$\frac{12x}{4} = $
2
Multiple Choice
+10 XP
$\frac{8x^3}{2x} = $
3
Multiple Choice
+10 XP
$\frac{6x^2y}{3xy} = $
4
Multiple Choice
+10 XP
$\frac{-15a^3}{5a} = $
5
Multiple Choice
+10 XP
A rectangle has area $12x^2$ and width $3x$. What is its length?
Show Your Working
9 marks total
Apply Medium 2 MARKS

Q6. Simplify $\frac{18x^2}{6x}$.

Answer in your workbook.
Apply Medium 3 MARKS

Q7. Simplify $\frac{-20a^3b^2}{4ab}$.

Answer in your workbook.
Apply Medium 4 MARKS

Q8. A triangle has area $\frac{1}{2} \times \text{base} \times \text{height}$. If the area is $15x^2$, the base is $5x$, find the height.

Answer in your workbook.
Apply Hard 3 MARKS

Stretch. If $\frac{30x^3}{kx} = 6x^2$, find the value of $k$.

Answer in your workbook.
Stretch Challenge · +25 XP, +10 coins

Extension Problems

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