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Recap: The Third Side

Part of the Triangles section of Coddy's Geometry journey. Lesson 14 of 71.

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Challenge

A triangle has sides 15, 8 and x.

A triangle with sides labelled 15, 8 and x

Find the range of x.

Try it yourself

15 - 8 < x < 15 + 8

Solve for x

All lessons in Triangles

1Sides and Names

Three Sides, Three CornersSorting by SidesNaming by AnglesTicks into EquationsThe Longest SideRecap: Sorting Triangles

4Area

Half the RectangleHeight Is Not a SideRight Triangle AreaFinding the HeightFinding the BaseAny Side Can Be the BaseRecap: Area

7Is It Right?

The ConverseTesting a TriangleAcute or Obtuse?Sorting by the TestRecap: Right or Not

10Scale in the World

ShadowsAcross the RiverA Side with an ExpressionNested TrianglesRecap: Scale in the World

2The Triangle Inequality

Can Three Sticks Meet?Exactly ReachingHow Short Can It Be?How Long Can It Be?The Range of the Third SideThe FormulaWhole-Number SidesRecap: The Third Side

5The Hypotenuse

Squares on the SidesFinding the HypotenusePythagorean TriplesWhen It Is Not WholeSimplifying the RootRecap: The Hypotenuse

8Special Right Triangles

The 45-45-90 TriangleLegs from the HypotenuseThe 30-60-90 TriangleAll Three SidesWhich Triangle Is It?Recap: Special Triangles

11Mixing Area and Pythagoras

Height of an IsoscelesArea from the HeightThe Equilateral TriangleRight Triangle PerimeterRecap: Two Tools

3Perimeter

Around the EdgeA Missing SideIsosceles PerimeterEquilateral PerimeterSides as ExpressionsWrite the PerimeterRecap: Around the Edge

6Finding a Leg

Working BackwardsThe LadderWhich Side Is c?A Leg That Is Not WholeRecap: Finding a Leg

9Similar Triangles

Same Shape, Different SizeThe Scale FactorFinding a SideThe Unknown BelowMatching the CornersRecap: Similar Triangles

12Final Challenges

Final: Three SticksFinal: The FenceFinal: The LadderFinal: The ShadowFinal: Master of Triangles