What you’ll learn
Find axis of symmetry.
Key idea
A vertical line has constant x, not constant y.
Symmetry axis uses constant x, not constant vertex output y.
Worked example
Enter the exact value or ordered values in the format requested below.
Find vertical axis of symmetry of y=-3(x+4)²-1. Enter x=number.
- Vertex is (-4,-1) because the inner square vanishes at x=-4.
- Equal offsets h±d have equal outputs -1+-3d², so the vertical symmetry line is x=-4.
Answer: x=-4
Quick Check
Evaluate a worked attempt at find axis of symmetry, identify the first invalid step, and provide the correction.
For y=-3(x+2)²+2, Step 1 finds vertex (-2,2). Step 2 selects y=2 as the vertical symmetry axis. Identify first invalid step and correct it.