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Grade 8 math worksheets

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Rewrite linear expressions

Learning goals

  • Uses distributive and combining-like-terms properties to rewrite linear expressions.
  • Produces equivalent simplified forms.
  • Chooses a form that reveals useful structure.
  • Checks equivalence by expansion or substitution.

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Rewrite linear expressions 1
Rewrite \(5(x + 2)\) in an equivalent form without parentheses.

Hints

- Which property lets you remove parentheses when a factor is outside them? - The outside factor applies to each term inside the parentheses. - After removing the parentheses, check that each original term has been accounted for.

Solution

Distribute \(5\) to both terms inside the parentheses: \(5(x + 2) = 5x + 10\).

Answer

\(5x + 10\)
Rewrite linear expressions 2
Rewrite \(-2(3x-4)\) without parentheses.

Hints

- Which two terms must the outside factor multiply? - What happens to each sign when you multiply by a negative number?

Solution

1. Multiply both terms in the parentheses by \(-2\). 2. The result is \(-6x+8\).

Answer

\(-6x+8\)
Rewrite linear expressions 3
Simplify \(3x+5+2x-8\) by combining like terms.

Hints

- Which terms contain the variable? - Which terms are numbers without a variable?

Solution

1. Combine the terms with \(x\): \(3x+2x=5x\). 2. Combine the constants: \(5-8=-3\). The expression becomes \(5x-3\).

Answer

\(5x-3\)
Rewrite linear expressions 4
Are \(4(x+1)\) and \(4x+4\) equivalent for every \(x\)? Explain why.

Hints

- How could you rewrite the expression with parentheses? - What must be true for expressions to be equivalent for every input?

Solution

1. Distribute in the first expression: \(4(x+1)=4x+4\). 2. Both expressions have the same value for every \(x\), so they are equivalent.

Answer

Yes. \(4(x+1)=4x+4\) for every \(x\) by the distributive property.
Rewrite linear expressions 5
Rewrite each expression in the form \(mx+b\): \(f(x)=2(x-3)+4\) and \(g(x)=5-\frac{1}{2}x-2\).

Hints

- Remove the parentheses in \(f\) using the distributive property. - Combine constant terms separately from variable terms. - Arrange each result with the \(x\)-term first and the constant second.

Solution

1. Distribute and combine constants in \(f\): \(f(x)=2x-6+4=2x-2\). 2. Combine constants in \(g\): \(g(x)=-\frac{1}{2}x+5-2=-\frac{1}{2}x+3\).

Answer

\(f(x)=2x-2\) \(g(x)=-\frac{1}{2}x+3\)
Rewrite linear expressions 6
The diagram shows a rectangle. Write an equivalent expression without parentheses for its area.
Figure for problem 551989

Hints

- Write the rectangle's area as length times width. - Use the distributive property to remove the parentheses.

Solution

1. The area is \(4(x + 3)\). 2. Distribute \(4\) to both terms inside the parentheses: \(4x + 12\).

Answer

\(4x + 12\) square units
Rewrite linear expressions 7
Cian rewrites \(5(2x - 3)\) as \(10x - 3\). Is the rewrite correct? If not, give the correct equivalent expression and explain the error.

Hints

- Check whether the outside factor affects every term inside the parentheses. - Compare the original and rewritten expressions term by term.

Solution

1. The rewrite is not correct because the factor \(5\) must multiply both terms inside the parentheses. 2. Distributing gives \(5(2x) - 5(3) = 10x - 15\).

Answer

No. The correct equivalent expression is \(10x - 15\). Cian multiplied only the first term by \(5\).
Rewrite linear expressions 8
Rewrite \(3(2x + 5) - 4x + 7\) as a single simplified linear expression.

Hints

- Remove the parentheses before combining terms. - Combine variable terms with variable terms and constants with constants.

Solution

1. Distribute \(3\): \(6x + 15 - 4x + 7\). 2. Combine like terms: \(6x - 4x = 2x\) and \(15 + 7 = 22\). 3. The simplified expression is \(2x + 22\).

Answer

\(2x + 22\)
Rewrite linear expressions 9
Riley says \(2(x+3)\) and \(3x+4\) are equivalent because both equal \(10\) when \(x=2\). Is Riley right? Use a different value of \(x\) to explain.

Hints

- What does equivalent mean beyond a single test value? - Can you choose an easy input different from \(2\)? - What would one pair of unequal results show?

Solution

1. When \(x=0\), the first expression equals \(6\) and the second equals \(4\). 2. Since the expressions differ at \(x=0\), they are not equivalent for every \(x\). One matching input is not enough.

Answer

No. At \(x=0\), the values are \(6\) and \(4\). They are not equivalent.
Rewrite linear expressions 10
Find \(a\) so that \(2(x+5)+3x\) is equivalent to \(ax+10\) for every \(x\). Explain your answer.

Hints

- Rewrite the expression with parentheses first. - What must stay the same for every value of \(x\)? - Compare the simplified expression with the form containing \(a\).

Solution

1. Rewrite the first expression: \(2(x+5)+3x=2x+10+3x=5x+10\). 2. Its coefficient of \(x\) must equal \(a\). Thus \(a=5\), and both expressions are \(5x+10\) for every \(x\).

Answer

\(a=5\). Both expressions simplify to \(5x+10\).
Rewrite linear expressions 11
Find \(k\) so that \(k(x+4)+2x\) and \(7x+20\) are equal for every \(x\). Show that both the coefficients of \(x\) and the constant terms match.

Hints

- What does it mean for two expressions to be equal for every value of \(x\)? - Rewrite the expression with \(k\) so its variable term and constant are easy to see. - Would checking just one value of \(x\) prove the two expressions equivalent?

Solution

1. Rewrite the first expression: \(k(x+4)+2x=(k+2)x+4k\). 2. Equivalent linear expressions have the same coefficient of \(x\) and the same constant term. 3. Comparing coefficients gives \(k+2=7\), so \(k=5\). Comparing constants gives \(4k=20\), also yielding \(k=5\). 4. With \(k=5\), both expressions simplify to \(7x+20\) for every \(x\).

Answer

\(k=5\). The coefficients match because \(k+2=7\), and the constants match because \(4k=20\).
Rewrite linear expressions 12
A rectangle has length \(2x + 1\) units and width \(x - 2\) units, where \(x > 2\). Write its perimeter as a single simplified linear expression.

Hints

- A rectangle has two lengths and two widths. - Write the perimeter expression before simplifying it. - Distribute first, then combine like terms.

Solution

1. Use the perimeter formula: \(P = 2(2x + 1) + 2(x - 2)\). 2. Distribute: \(P = 4x + 2 + 2x - 4\). 3. Combine like terms: \(P = 6x - 2\).

Answer

\(6x - 2\) units

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