Two-step equations

Site: Saylor Academy
Course: GKT101: General Knowledge for Teachers – Math
Book: Two-step equations
Printed by: Guest user
Date: Sunday, May 19, 2024, 2:45 PM

Description

Two-step equations can also be solved by "undoing" each operation by applying its inverse to both sides of the equation. Watch this lecture series and complete the interactive exercises.

Two-step equations intuition

Worked example: two-step equations

Describing steps when solving equations

Two-step equations - Questions

1. Solve for p.

9(p−4)=−18


2. Solve for m.

13=2m+5


3. Solve for y.

6=2(y+2)


4. Solve for g.

3=\frac{g}{-4}-5


5. Solve for z.

42=−7(z−3)


6. Solve for d.

41=12d−7


7. Solve for q.

3(q−7)=27

Answers

1. p = 2

Let's divide and then add to get p by itself.

 9(p-4)=-18

divide each side by 9

\begin{array}{r}
\frac{9(p-4)}{9}=\frac{-18}{9} \\
\frac{g(p-4)}{9}=\frac{-18}{9} \\
p-4=\frac{-18}{9}
\end{array}


p−4 = - 2

add 4 to each side to get p by itself

\begin{array}{r}
p-4+4=-2+4 \\
p-4+4=-2+4 \\
p=-2+4
\end{array}

The answer: p = 2


Let's check our work!

\begin{array}{r}
9(p-4)=-18 \\
9(2-4) \stackrel{?}{=}-18 \\
9(-2) \stackrel{?}{=}-18 \\
-18=-18 \text { Yes! }
\end{array}


2. m = 4

Let's subtract and then divide to get m by itself.

13=2m+5

subtract 5 from each side

\begin{aligned}
&13-5=2 m+5-5 \\
&13-5=2 m+5-\not 5 \\
&13-5=2 m
\end{aligned}


8 = 2m

divide each side by 2 to get m by itself

\begin{aligned}
&\frac{8}{2}=\frac{2 m}{2} \\
&\frac{8}{2}=\frac{2 m}{2} \\
&\frac{8}{2}=m
\end{aligned}

The answer: m = 4


Let's check our work!

\begin{aligned}
&13=2 m+5 \\
&13 \stackrel{?}{=} 2(4)+5 \\
&13 \stackrel{?}{=} 8+5 \\
&13=13 \quad \text { Yes! }
\end{aligned}


3. y = 1

Let's divide and then subtract to get y by itself.

6=2(y+2)

divide each side by 2

\begin{aligned}
&\frac{6}{2}=\frac{2(y+2)}{2} \\
&\frac{6}{2}=\frac{2(y+2)}{2} \\
&\frac{6}{2}=y+2
\end{aligned}


3 = y +2

subtract 2 to get y by itself

\begin{aligned}
&3-2=y+2-2 \\
&3-2=y+\not 2-2 \\
&3-2=y
\end{aligned}

The answer: y = 1


Let's check our work!

\begin{aligned}
&6=2(y+2) \\
&6 \stackrel{?}{=} 2(1+2) \\
&6 \stackrel{?}{=} 2(3) \\
&6=6 \quad \text { Yes! }
\end{aligned}


4. g = -32

Let's add and then multiply to get g by itself.

3=\frac{g}{-4}-5

add 5 to each side

\begin{aligned}
&3+5=\frac{g}{-4}-5+5 \\
&3+5=\frac{g}{-4}-5+5 \\
&3+5=\frac{g}{-4}
\end{aligned}


8=\frac{g}{-4}

multiply each side by −4 to get g by itself

8 \cdot-4=\frac{g}{-4} \cdot-4

8 \cdot-4=\frac{g}{-\not 4} \cdot -\not 4

8 \cdot-4=g


Let's check our work!

\begin{aligned}
&3=\frac{g}{-4}-5 \\
&3 \stackrel{?}{=} \frac{-32}{-4}-5 \\
&3 \stackrel{?}{=} 8-5 \\
&3=3 \quad \text { Yes! }
\end{aligned}


5.  z = -3

Let's divide and then add to get z by itself.

42=−7(z−3)

divide each side by −7

\begin{aligned}
&\frac{42}{-7}=\frac{-7(z-3)}{-7} \\
&\frac{42}{-7}=\frac{7(z-3)}{-7} \\
&\frac{42}{-7}=z-3
\end{aligned}


 -6 = z - 3

add 3 to each side to get z by itself

\begin{aligned}
&-6+3=z-3+3 \\
&-6+3=z-\not 3+ \not 3 \\
&-6+3=z
\end{aligned}

The answer: z = -3


Let's check our work!

\begin{aligned}
&42=-7(z-3) \\
&42 \stackrel{?}{=}-7(-3-3) \\
&42 \stackrel{?}{=}-7(-6) \\
&42=42 \quad \text { Yes! }
\end{aligned}


6. d = 4

Let's add and then divide to get d by itself.

41=12d−7

add 7 to each side

\begin{aligned}
&41+7=12 d-7+7 \\
&41+7=12 d-\not 7+ \not 7 \\
&41+7=12 d
\end{aligned}


48 = 12d

\begin{aligned}
&\frac{48}{12}=\frac{12 d}{12} \\
&\frac{48}{12}=\frac{ \not {12} d}{\not {12}} \\
&\frac{48}{12}=d
\end{aligned}

The answer: d = 4


Let's check our work!

\begin{aligned}
&41=12 d-7 \\
&41 \stackrel{?}{=} 12(4)-7 \\
&41 \stackrel{?}{=} 48-7 \\
&41=41 \quad \text { Yes! }
\end{aligned}


7.  q = 16

Let's divide and then add to get q by itself.

3(q−7)=27

divide each side by 3

\begin{aligned}
&\frac{3(q-7)}{3}=\frac{27}{3}\\
&\frac{\not 3(q-7)}{\not 3}=\frac{27}{3}\\
&q-7=\frac{27}{3}
\end{aligned}


q - 7 = 9

add 7 to each side to get q by itself

\begin{array}{r}
q-7+7=9+7 \\
q-7+7=9+7 \\
q=9+7
\end{array}

The answer:  q = 16


Let's check our work!

\begin{aligned}
3(q-7) &=27 \\
3(16-7) & \stackrel{?}{=} 27 \\
3(9) & \stackrel{?}{=} 27 \\
27 &=27 \quad \text { Yes! }
\end{aligned}