Graphing Quadratics in Standard Form
I can graph y = ax² + bx + c by finding the axis of symmetry and the vertex first.
What students learn
Students learn to find the axis of symmetry x = −b/(2a) and the vertex, give the y-intercept and the direction, and use symmetry to plot points and graph a parabola.
See inside
The key rule
Find the axis x = −b/(2a) first; the vertex is on it. Points the same distance from the axis have the same height.
y = ax² + bx + c; axis x = −b/(2a)
The sign of a, not c, says which way the parabola opens.
Watch out
A student says the axis of symmetry of y = x² − 6x + 5 is x = −3.
The mistake: −6/(2 · 1) = −3b is −6, so −b is +6: the minus was dropped.
The fix: −(−6)/(2 · 1) = 3: axis x = 3x = 2 and x = 4 both give −3, and 3 is halfway.
The mistakes it targets
- Drops the minus in x = −b/(2a)
- Reads the direction of opening from c instead of a
- Mirrors points across the y-axis instead of the axis of symmetry
- Divides by a instead of 2a
- Squares a negative input without parentheses
The interactive Teacher Deck (32 slides, PowerPoint)
- The Learn page taught on screen: 8 fill-in blanks, each filled on its own click as students write it
- The worked example one slide per step (four steps), each with the reason for the step
- Six practice and three apply problems: a your-turn slide with a think-time bar, then the solution one line per click
- Jump buttons on every slide: go straight to any problem, the answer bank or the exit ticket
- Speaker notes on each problem: the question to ask, the worked answer and the common error to listen for
- A completed deck PDF (19 pages) with every slide fully built, to print or post
The student packet (9 pages)
- Learn: guided notes with four definitions, the key rule, a worked example and a Watch Out error pair
- Practice: two warm-up, two standard and two stretch problems, with an answer bank for self-checking that hides three common-mistake decoys
- Apply: one word problem, a reasoning prompt and one error analysis
- Assess: an exit ticket of four items, two per page, with an I-can self-rating
- Homework (page 5): eight new problems, two warm-up, four standard and two stretch
- Answer key (pages 6–7): every problem worked step by step, five common mistakes with what to do about each, and a grading guide, plus the homework key (page 8)
- Color and ink-saver editions of the whole packet
Standard codes refer to the Common Core State Standards for Mathematics. Math Class 678 is an independent publisher, not affiliated with, sponsored by, or endorsed by NGA Center or CCSSO. Every product is sold on Teachers Pay Teachers.