Conic Sections: Recognizing the Four Curves
Recognize and analyze the conic sections — circle, ellipse, parabola, and hyperbola — by their equations, for the ACT and Pre-Calculus, with worked problems.
The Short Version
- The four conic sections are the circle, ellipse, parabola, and hyperbola.
- Ellipse: x²/a² + y²/b² = 1 (both squared, added, different denominators).
- Hyperbola: x²/a² − y²/b² = 1 (a minus between the squared terms).
- Identify by the equation's form: added = ellipse/circle; subtracted = hyperbola; one squared term = parabola. An ACT/Pre-Calc topic.
If you slice a cone at different angles, the edge of the cut traces one of four curves: a circle, an ellipse, a parabola, or a hyperbola. That's why they're called "conic sections." You've already met circles and parabolas; the ellipse (a stretched circle) and the hyperbola (two opening branches) complete the family. For the ACT and an introductory course, the key skill is simply recognizing which conic an equation describes — and a few clues make that quick.
This guide covers all four conics and how to tell them apart, with worked and practice problems matched to real test difficulty at Northside Tutoring.
Why Conics Matter
Conic sections appear on the ACT and are a Pre-Calculus unit. Most test questions ask you to identify the conic from its equation or read off basic features (center, radius, axes). They build on the circle equation and parabola work you've done. (Beyond the SSAT; rare on the SAT.)
The Four Conics
The whole family, by equation signature:
| Conic | Equation signature |
|---|---|
| Circle | x² + y² terms, equal coefficients |
| Parabola | only one variable squared |
| Ellipse | both squared, added, different denominators |
| Hyperbola | both squared, subtracted |
Circle & Parabola (Review)
You've met two already. A circle is (x − h)² + (y − k)² = r² — both terms squared and added, with equal "weight." A parabola has just one variable squared, like y = a(x − h)² + k — it opens in one direction.
The Ellipse
An ellipse is a stretched circle; a and b are the semi-axes along the two directions.
An ellipse is like a circle stretched in one direction. Its standard equation has both variables squared and added, but with different denominators:
(When a = b, it's just a circle.) The larger denominator's axis is the longer one.
The Hyperbola
A hyperbola looks like two curves opening away from each other. Its equation is just like an ellipse's but with a minus sign between the squared terms:
That single minus is what separates a hyperbola from an ellipse.
Identifying a Conic
The quick identification clues
Only one variable squared → parabola. Both squared and added: equal coefficients → circle, different → ellipse. Both squared and subtracted → hyperbola. The signs and coefficients tell you everything.
Where You'll See This — Test by Test
No reference sheet covers conics. The ACT tests identifying conics from equations and basic features; they're a Pre-Calculus unit. Rare on the SAT, and beyond the SSAT.
ACT
Tests identifying conics from their equations and reading features like center and axes.
Explore ACT Tutoring → College AdmissionsSAT
Conics beyond circles/parabolas are rare on the SAT; this is more of an ACT and Pre-Calculus topic.
Explore SAT Tutoring → K-12 CurriculumPre-Calculus
Conic sections are a standard Pre-Calculus unit, including foci and directrices.
Explore Math Tutoring → K-12 CurriculumAlgebra II
Builds on the circle equation and parabola work from Algebra II.
Explore Algebra Tutoring →Watch the Lesson
Sometimes a diagram needs a voice. In the short video below, one of our Northside tutors walks through the core idea and works through test-style problems in real time.
Conic Sections — In Plain English
A live walkthrough from our tutoring team.
— Featuring a Northside Tutoring instructor
Worked Example Problems
These problems are calibrated to the difficulty you'll actually see on test day. Try each one before opening the solution.
What conic is x²/9 + y²/4 = 1?
Show solution
Both squared, added, different denominators — an ellipse.
What conic is x²/16 − y²/9 = 1?
Show solution
Both squared with a minus between them — a hyperbola.
What conic is x² + y² = 25?
Show solution
Both squared, added, equal coefficients — a circle (radius 5).
What conic is y = 2x² − 3?
Show solution
Only x is squared — a parabola.
For the ellipse x²/25 + y²/9 = 1, along which axis is it longer?
Show solution
The larger denominator (25) is under x², so the ellipse is longer along the x-axis (semi-axis 5 vs. 3).
Common Mistakes to Avoid
Three traps that catch students every year
- Missing the minus sign. Added squared terms make an ellipse/circle; a subtracted term makes a hyperbola.
- Confusing circle and ellipse. Equal coefficients/denominators → circle; different → ellipse.
- Forgetting the axes come from a² and b². The semi-axis is the square root of the denominator, not the denominator itself.
Practice Problems — You Try
Three problems below. Work each before checking the solution.
Identify: y²/4 − x²/9 = 1.
Show solution
Both squared, subtracted — a hyperbola.
Identify: (x − 1)² + (y + 2)² = 16.
Show solution
Both squared, added, equal coefficients — a circle (center (1, −2), radius 4).
Identify and give the semi-axes: x²/36 + y²/100 = 1.
Show solution
Both squared, added, different denominators — an ellipse. Semi-axis along x is √36 = 6; along y is √100 = 10, so it's taller than it is wide.
The Northside Method — How We Teach This 1-on-1
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Every Northside student works through a four-step framework:
- Assessment. We diagnose which specific skills are slowing your student down — not just whether they "get it" in the abstract.
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