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How to Solve Linear Functions

Linear functions show up everywhere: prices, distance, growth, and more. Once you understand slope and intercepts, you can solve and graph them quickly.

📈 Algebra⏱️ ~16 min read🟢 Beginner

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What Is a Linear Function?

A linear function is a function whose graph is a straight line. The most common form is y = mx + b.

  • m is the slope (rate of change): how much y changes when x increases by 1.
  • b is the y-intercept: the value of y when x = 0.

If your task is to solve a linear equation in one variable (like 3x + 5 = 14), start with how to solve linear equations step by step. Linear functions often use the same algebra, but they add interpretation (slope, intercepts, and graphs).

Core Skills for Linear Functions

1) Evaluate f(x)

Substitute an x-value and compute the output.

f(x) = 2x - 3
f(5) = 2(5) - 3 = 7

2) Solve f(x) = y

Set the function equal to a given output and solve for x.

f(x) = 2x - 3
2x - 3 = 11
2x = 14
x = 7

How to Find Slope and Intercepts

From slope-intercept form

If you already have y = mx + b, then:

  • Slope is m
  • y-intercept is b

From standard form

Standard form is Ax + By = C. You can find intercepts quickly:

Example: 3x + 2y = 12

  • x-intercept: set y = 0 → 3x = 12 → x = 4 → point (4, 0)
  • y-intercept: set x = 0 → 2y = 12 → y = 6 → point (0, 6)

If you want to practice converting to y = mx + b, the next guide focuses on that: how to solve slope intercept form.

Worked Example (Word Problem)

A gym charges $20 to join and $15 per month.

Let x = months and y = total cost. The join fee is a starting amount, so it’s the intercept.

y = 15x + 20

Question: How many months until the cost reaches $110?

15x + 20 = 110
15x = 90
x = 6

Interpretation: after 6 months, the total cost is $110.

Common Mistakes

Mixing up slope and intercept

In y = mx + b, m is attached to x. b is the constant. If there’s no x, it’s not slope.

Sign errors when solving

When you move terms, remember you’re adding/subtracting the same amount on both sides.

Forgetting what the variables mean

In word problems, define x and y. The same equation can mean different things in different contexts.

Thinking “solve” always means “find x”

For functions, you might be asked to evaluate f(3), find intercepts, or interpret slope.

If you’d like a few more graph-and-slope examples in the same style, Khan Academy’s linear equations & graphs unit is a good reference.

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How to Solve Linear Functions | Slope, Intercepts, Graph