Prerequisites: Reviewing Geometry

Self Check Angle and Triangle Self Check

Now, you try. Complete the self-check activity by looking at the questions below, working them out, and then clicking on the question to review the solution.

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Which angles in the image below are congruent? How do you know?

Angles 1 and 3 and angles 2 and 4 are congruent. They are vertical angles.

Two intersecting lines with angles labeled 1,2,3,4 starting in up left going clockwise.

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Is triangle A B C similar to triangle D E F? Why?

Yes, they are similar triangles. They have two angles of the same measure, but are not the same size.

Two triangles. Triangle ABC, angle A is forty degrees and angle B is 80 degrees and triangle DEF, angle D is forty degrees and angle E is 80 degrees.

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Using the diagram below, name an acute, an obtuse, a right, and a straight angle.
Acute
angle A OB, Angle B O C, angle C O D , angle D O E
Obtuse
angle A O D , angle B O E
Right
angle A O C angle B O D angle C O E
Straight
angle A O E

Straight angle AOE, Ray OC is at a right angle to angle AOE. Angle BOD is a right angle. Angle B is interior to angle AOC and angle D is interior to angle EOC.

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Are the triangles below congruent? Why?
Yes, by the theorem side-angle-side they can be proven congruent.

Two right triangles with one tick mark on the hypotenuse and two tick marks on the shortest sides and the same angle indicator on the included angle.