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Algebra I: Linear functions

Grade 8 · Math · Free lesson

Hey there! Ready to discover the magic of linear functions? We are going to see how math can help us predict patterns that grow at a steady, constant speed!

A linear function is just a rule that connects an input number to an output number. The coolest part is that it always changes by the exact same amount every single step, creating a perfectly straight line!

geometry

Think of a linear function like a steady staircase. Every step you take forward (the input, x), you climb up by the exact same height (the output, y). This constant rate of climbing is what mathematicians call the 'slope'!

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We write these functions in a special format called Slope-Intercept form: y = mx + b. Here, m is our slope (how steep the line is), and b is our y-intercept (where the line crosses the vertical y-axis to start).

y-intercept (b) y = mx + b
✏️ Worked example

A young maple tree is 3 feet tall when planted. Each year, it grows exactly 2 feet. Write a linear equation to find the height of the tree (y) after any number of years (x).

  1. 1. Identify the starting value (the y-intercept, b). Since the tree starts at 3 feet tall, b = 3.
  2. 2. Identify the rate of change (the slope, m). Since the tree grows 2 feet every year, the constant rate is 2, so m = 2.
  3. 3. Plug these values into the slope-intercept form equation: y = mx + b.
  4. 4. Replace m with 2 and b with 3 to get our final equation: y = 2x + 3.
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