standard_description: Prove theorems about parallelograms. Theorems include: opposite sides are congruent, opposite angles are congruent, the diagonals of a parallelogram bisect each other, and conversely, rectangles are parallelograms with congruent diagonals.
problem_activity: Warm-up
In this activity, students practice determining the measurement of unknown angles using their relationship to angles with known angle measure and what students already know about the measurement of right angles and straight angles. After they have worked on the activity and shared their solutions, they are introduced to the vocabulary terms complementary and supplementary. Complementary describes angles whose measures sum to 90 degrees and supplementary describes angles whose measures sum to 180 degrees.
Some students may wish to use protractors, either to double check work or to investigate the different angle measures. This is an appropriate use of technology (MP5), but ask these students what other methods they could use instead.
Launch
Provide access to geometry toolkits.
Student Facing
Find the measure of angle
\(JGH\)
. Explain or show your reasoning.
[IMG]
Find and label a second
\(30^\circ\)
angle in the diagram. Find and label an angle congruent to angle
\(JGH\)
.
Angle
\(BAC\)
is a right angle. Find the measure of angle
\(CAD\)
.
[IMG]
​​​​​
Student Response
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Anticipated Misconceptions
If needed, remind students that right angles have a measure of
\(90^\circ\)
and straight angles have a measure of
\(180^\circ\)
.
Activity Synthesis
The goal of this discussion is to introduce students to the terms complementary and supplementary for describing relationships between pairs of angles. Display the images for all to see and select students to briefly share their response to each question, recording any calculations used.
Explain to students that the term
complementary
describes a pair of angles whose measures sum to 90 degrees, and the term
supplementary
describes a pair of angles whose measures sum to 180 degrees. This is true even for pairs of angles that are not adjacent. Conclude the discussion by inviting students to identify pairs of angles that are complementary (
\(CAD\)
and
\(DAB\)
), supplementary (
\(FGJ\)
and
\(JGH\)
,
\(JGH\)
and
\(HGI\)
,
\(HGI\)
and
\(IGF\)
, or
\(IGF\)
and
\(FGJ\)
), or vertical (
\(FGJ\)
and
\(HGI\)
or
\(JGH\)
and
\(IGF\)
) from the activity.


aligns: no