Angle relationships and unknown angle problems (7th grade math)

The first video has to do with supplementary angles. If two angles share a side and together form a straight line (180 degrees), they are supplementary. We look at this principle and then apply it in a few exercises. As a mnemonic, Supplementary angles form a Straight line, whereas Complementary angles form a Corner (90 degrees).

In the second video, we look at vertical angles. When two lines intersect, two pairs of vertical angles are formed. Vertical angles are equal (or congruent). We explore applications of this principle, finding unknown angle measures in figures.

In the last video, I solve an "angle puzzle" where several angles share a vertex, several angles are unknown, marked with x or x + 14. Using the principles of vertical and supplementary angles enables us to write an equation to solve for x, and from there to find the measures of the unknown angles.

See also

Circumference of a Circle — video lesson

Math Mammoth Geometry 3 — a self-teaching worktext with explanations & exercises (grades 4-5)

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