Acute, Obtuse, and Right Triangles
This is a free geometry lesson for 4th grade about acute, obtuse, and right triangles (classification according to angles). It contains varied exercises, including several where students explore these concepts -- and even the angle sum of a triangle -- by drawing.
![]() ![]() right angles |
obtuse angles |
acute angles |
|
Obtuse triangles have |
Acute triangles have three |
1. a. Draw a right angle.
Then b. Draw another,
different
c. A right
triangle has one right
|
|
A right triangle has one right angle. The other two angles are _____________________. |
2. a. Draw an obtuse angle.
|
|
b. Draw another,
different c. An
obtuse triangle has one |
An obtuse triangle has one obtuse angle. The other two angles are _____________________. |
3. a. Draw an acute triangle.
b. Measure its angles.
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4. Observe all you have done thus far in this lesson, and fill in.
Right triangles have exactly 1 _________________ ________________, and the other two angles are _________________ . Obtuse triangles have exactly 1 _________________ ________________, and the other two angles are _________________ . Acute triangles have ___ ____________ angles. |
5. Label the triangles in the pictures as right, acute, or obtuse.
a. |
b. |
c. |
d. |
e. |
f. |
g. |
7. a. Draw a triangle with
Hint: First draw a 85° angle. b.
Measure the third angle. c. What kind of triangle
is it? d. What is the angle sum? |
|
b.
Measure the third angle. c. What kind of triangle is it? d. What is the angle sum? |
|
9. a. Draw a triangle with b. Measure the third
angle. c. What kind of triangle is it? d. What is the angle sum?
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This lesson is taken from Maria Miller's book Math Mammoth Geometry 1, and posted at www.HomeschoolMath.net with permission from the author. Copyright © Maria Miller.
Math Mammoth Geometry 1
A self-teaching worktext for 4th-5th grade that covers angles, triangles, quadrilaterals, cirlce, symmetry, perimeter, area, and volume. Lots of drawing exercises!
Download ($6.90). Also available as a printed copy.