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Algebra - Solving Linear Equations in One Variable

Grade 8IB

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

A Linear Equation in one variable is an algebraic equation where the exponent of the variable is exactly 11. Visually, if represented on a coordinate plane as y=mx+cy = mx + c, it would form a perfectly straight line.

The Equality Principle functions like a balance scale. To keep the equation true, any mathematical operation performed on the Left Hand Side (LHS) must also be performed on the Right Hand Side (RHS). Imagine adding weights to both sides of a scale to keep it level.

Isolation of the Variable is the primary goal of solving equations. This involves using inverse operations to move all constants to one side and the variable to the other, resulting in the form x=valuex = \text{value}.

Inverse Operations are pairs of mathematical operations that undo each other. Addition is the inverse of subtraction (e.g., to remove 5-5, add +5+5), and multiplication is the inverse of division (e.g., to remove a denominator of 33, multiply by 33).

The Distributive Property is used when an equation contains parentheses, such as a(x+b)=ca(x + b) = c. You must multiply the term outside the bracket by every term inside, visually expanding the expression to ax+ab=cax + ab = c before solving.

Variables on Both Sides require grouping like terms. If you see axax on the left and cxcx on the right, subtract one of the variable terms from both sides so that the variable exists only on one side of the 'equals' sign.

Clearing Fractions is a technique used when equations involve denominators. By multiplying the entire equation by the Least Common Multiple (LCM) of all denominators, you can transform a fractional equation into a simpler linear form without fractions.

📐Formulae

Standard form of a linear equation: ax+b=0ax + b = 0

Distributive Law: a(b+c)=ab+aca(b + c) = ab + ac

Cross-multiplication for proportions: If ab=cd\frac{a}{b} = \frac{c}{d}, then ad=bcad = bc

Addition/Subtraction property: If a=ba = b, then a+c=b+ca + c = b + c and ac=bca - c = b - c

Multiplication/Division property: If a=ba = b, then ac=bcac = bc and ac=bc\frac{a}{c} = \frac{b}{c} (where c0c \neq 0)

💡Examples

Problem 1:

Solve for xx: 4(x3)=2x+104(x - 3) = 2x + 10

Solution:

4x12=2x+104x - 12 = 2x + 10 4x2x12=104x - 2x - 12 = 10 2x12=102x - 12 = 10 2x=10+122x = 10 + 12 2x=222x = 22 x=222x = \frac{22}{2} x=11x = 11

Explanation:

First, apply the distributive property to expand the left side. Next, collect the variable terms on the left side by subtracting 2x2x from both sides. Then, isolate the xx term by adding 1212 to both sides. Finally, divide by the coefficient 22 to find the value of xx.

Problem 2:

Solve for yy: y+53=4\frac{y + 5}{3} = 4

Solution:

3(y+53)=433 \cdot \left(\frac{y + 5}{3}\right) = 4 \cdot 3 y+5=12y + 5 = 12 y=125y = 12 - 5 y=7y = 7

Explanation:

To solve this, we must first remove the fraction by performing the inverse of division. Multiply both sides of the equation by 33. This leaves us with a simple one-step equation. Subtract 55 from both sides to isolate yy.