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Recap: Models

Part of the Quadratics & Complex Numbers section of Coddy's Algebra 2 journey. Lesson 43 of 48.

Challenge

A ball is thrown up from the top of a 20 metre building. Its height after t seconds is $-5{t}^{2}+15t+20$ metres. The board holds the equation for height 0, the moment it hits the ground: solve it. You will find two answers, but only the positive time makes sense, since the ball was thrown at t = 0.

Try it yourself

-5t^{2}+15t+20 = 0

Get $t$ alone

All lessons in Quadratics & Complex Numbers

1The Vertex

The Axis of Symmetry Drawing from Standard Form Maximum or Minimum Recap: The Vertex

4Imaginary Numbers

Meet i Roots of Negatives Not a Perfect Square Powers of i Recap: Imaginary Numbers

7The Discriminant

Computing It Three Kinds of Answers Reading the Sign Recap: The Discriminant

10Final Challenges

Final: Square It Away Final: The Peak Final: Divide It Final: No Real Roots Final: Where They Meet

2Completing the Square

The Missing Number Completing the Square When a Is Not 1 Recap: Completing the Square

5Complex Arithmetic

Adding and Subtracting Multiplying The Conjugate Dividing A Pure Imaginary Bottom Recap: Complex Arithmetic

8Lines Meet Parabolas

Two Crossings Just Touching No Meeting A Circle and a Line Recap: Lines and Parabolas

3Vertex Form by Algebra

From Standard to Vertex Odd Middle Terms A Leading Number Opening Down Recap: Vertex Form

6Complex Solutions

Squares Equal to Negatives A Shifted Square The Formula Goes Complex Fractions in the Answer Recap: Complex Solutions

9Quadratic Models

The Highest Point Back to the Ground The Biggest Area Price and RevenueRecap: Models