Coefficients: The Controls Behind Every Graph

Change a number, change the shape. You're in charge.

Part 1

What's a Coefficient?

A coefficient is a number that multiplies a variable. In y = 3x + 2, the 3 is a coefficient - it controls how steep the line is. Change it, and the whole graph changes.

Think of coefficients as control knobs on a graph. Each knob does something different: one controls steepness, another controls position, another controls shape. In this lesson, you'll learn what each knob does.

y = 3x + 2
The coefficient 3 controls steepness
m
Slope
Steepness of the line
b
Y-Intercept
Where the line crosses y-axis
a
Leading Coefficient
Opens up/down, wide/narrow
'
y = 0.5x
0.5 is gentle
'
y = 1x
1 is moderate
'
y = 3x
3 is steep
Every equation has hidden controls. Learning what each coefficient does gives you the power to predict what a graph looks like without plotting a single point.
Part 2

Linear: y = mx + b

The simplest function family. Two coefficients, two controls: m for slope (steepness) and b for y-intercept (where it crosses the y-axis).

y = mx + b
m controls slope, b controls y-intercept
run:1rise:m'
m - The Slope
How steep the line climbs or falls
'
b - The y-intercept
Where the line crosses the y-axis

Drag the sliders to see how each coefficient controls the line. Use the ghost button to snapshot the current curve, then change a slider to see the difference.

Explore y = mx + b
y = 1x + 0
Part 3

Quadratic: y = a(x - h)^2 + k

Quadratics make parabolas - those U-shaped (or upside-down U) curves. Three coefficients, three controls: a for stretch & direction, h for horizontal shift, k for vertical shift.

y = a(x - h)^2 + k
Vertex at (h, k)
'
a - Stretch / Flip
Opens up or down, wide or narrow
'
h - Left / Right
Slides the vertex horizontally
'
k - Up / Down
Slides the vertex vertically

The vertex - the tip of the parabola - always sits at the point (h, k). The dashed line through the vertex is the axis of symmetry.

Explore y = a(x - h)^2 + k
y = 1(x 0)² + 0
This form is called vertex form because you can read the vertex directly from h and k. No calculation needed!
Part 4

Standard Form: y = ax^2 + bx + c

Standard form is the other common way to write a quadratic. Instead of seeing the vertex directly, you see three coefficients: a (same as vertex form - stretch & direction), b (the linear coefficient), and c (the y-intercept).

y = ax^2 + bx + c
x = -b / (2a) gives the vertex x-coordinate
'
a - Stretch / Flip
Same as vertex form
'
b - Linear Coefficient
Tilts and shifts the vertex
'
c - y-intercept
Where the curve crosses the y-axis

The vertex isn't obvious from this form, but you can find it: x = -b / (2a). The explorer below computes it live and shows the equivalent vertex form so you can compare.

Explore y = ax^2 + bx + c
y = 1x² + 0x + 0
Both forms describe the same parabola - just with different "knobs" exposed. Vertex form makes the vertex easy to read. Standard form makes the y-intercept obvious (it's just c).
Reference

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Test Your Understanding

Two mini-games to check what you learned. Match a hidden graph by adjusting coefficients, or solve a one-move challenge.

Match the Mystery Graph
Closeness2%
One-Move Challenge
Challenge 1 of 8
Make the line twice as steep