Problem 691: Isosceles Triangle, 808020 Degrees, Angles,
Congruence, Mind Map, Polya.
Level: High School, College, Math Ed.
The figure shows an isosceles triangle ABC with AB = BC and angle B = 20°.
Points D and E are on AB and BC, respectively so that the
measure of angle CAE is 40 degrees and the measure of angle ACD
is 50 degrees. DE and AC meet at F. Find the measure of angle
AFD.
Geometry problem solving
Geometry problem solving is one of the most
challenging skills for students to learn. When a
problem requires auxiliary construction, the
difficulty of the problem increases drastically,
perhaps because deciding which construction to
make is an illstructured problem. By
“construction,” we mean adding geometric figures
(points, lines, planes) to a problem figure that
wasn’t mentioned as "given."
How to Solve It, Interactive Mind Map
George Pólya's 1945 book "How to Solve It, A new
aspect of Mathematical Method", is a book
describing methods of problem solving. It
suggests the following steps when solving a
mathematical problem: (1) First, you have to
understand the problem. (2) After understanding,
then make a plan. (3) Carry out the plan. (4)
Look back on your work. How could it be better? Mind Map Help. To see a note: Hover over a yellow note button. To Fold/Unfold: click a branch. To Pan: click and drag the map canvas.

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