Same Shape, Different Size
Part of the Triangles section of Coddy's Geometry journey. Lesson 44 of 63.
Two triangles are similar when one is a scaled copy of the other: the same shape, any size. Their angles match exactly, and every side of one is the same number of times its partner in the other. The sign ~ means similar.
The order of the letters tells you which corners match. △ABC ~ △DEF says A matches D, B matches E and C matches F, so side AB matches DE and side CA matches FD. Here every side of △DEF is twice its partner.
The letters do not have to come in alphabetical order. △ABC ~ △QRP pairs A with Q, B with R and C with P. Always match by position in the name.
Challenge
The two triangles are similar: △ABC ~ △RPQ. Tap the corner of the big triangle that matches B, then press Check.
Try it yourself
Find the right part on the figure
Test yourselfThis lesson includes a short quiz. Start the lesson to answer it and track your progress.
All lessons in Triangles
1Sides and Names
Three Sides, Three CornersSorting by SidesNaming by AnglesTicks into EquationsThe Longest SideRecap: Sorting Triangles2The Triangle Inequality
Can Three Sticks Meet?Exactly ReachingThe Range of the Third SideThe FormulaRecap: The Third Side5The Pythagorean Theorem
Squares on the SidesFinding the HypotenusePythagorean TriplesWhen It Is Not WholeRecap: The Hypotenuse3Perimeter
Around the EdgeA Missing SideIsosceles PerimeterSides as ExpressionsRecap: Around the Edge6Finding a Leg
Working BackwardsThe LadderWhich Side Is c?A Leg That Is Not WholeRecap: Finding a Leg9Similar Triangles
Same Shape, Different SizeThe Scale FactorFinding a SideMatching the CornersRecap: Similar Triangles