Cogito
Grade 4 Math · Chapter 7 · Lesson 2
Naming and Measuring Angles
Acute, right, obtuse, straight.
10 problems · about 15 minutes · 4.MD.C.6
What this lesson teaches
The child measures an angle with a protractor and names it by type.
- Acute is less than 90 degrees, obtuse is more.
- A straight angle is exactly 180.
- Estimate first, then read the protractor.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
2 problemsReview — An Angle Is a Turn: How many degrees is a half turn?
Answer 180
Why 180 degrees, a straight line.
Review — Decimals and Money: How many cents is $0.35?
Answer 35
Why 35 cents.
Warm Up
Straightforward practice. Get the method working first.
4 problemsIs 75 degrees acute or obtuse?
Answer Acute.
Why 75 degrees is acute.
Why estimate before reading the protractor?
Answer It catches a reading off the wrong scale.
Why Knowing whether it beats 90 tells you which scale to read.
Is 30 degrees acute or obtuse?
Answer Acute.
Why Less than 90.
Is 100 degrees acute or obtuse?
Answer Obtuse.
Why More than 90.
Build It Up
The same ideas with more to keep track of.
2 problemsHow many degrees is a straight angle?
Answer 180
Why A half turn.
How many degrees is a right angle?
Answer 90
Why A quarter turn.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
2 problemsThe Name: An angle measures 55 degrees. What type is it?
Answer Acute.
Why 55 degrees is acute.
The Other Name: An angle measures 135 degrees. What type is it?
Answer Obtuse.
Why 135 degrees is obtuse.