What this lesson shows
Acute, right, obtuse, straight, reflex, tested against a paper corner.
The worked example
The lesson works this one step by step: 35°, 130°, 250°. Then your kid tries one like it on paper.
The steps
- Test with a paper corner
- Less than 90°: acute
- Up to 180°: obtuse
- Past 180°: reflex
Helping at home
Compare each angle with 90° and 180°. Less than 90° is acute, exactly 90° is right, between 90° and 180° is obtuse, exactly 180° is straight, and more than 180° is reflex. With a drawn angle, hold the corner of a sheet of paper on it.
If your kid gets stuck
Is it less than 90°, between 90° and 180°, or more?
Watch it with Lux
With Lux, this lesson is a narrated video and a printed page your kid works on. Then Lux helps with the same math on their own worksheet, one question at a time.
Standards
- Common Core 4.MD.C.5
Recognize angles as geometric shapes that are formed wherever two rays share a common endpoint, and understand concepts of angle measurement: - Common Core 4.G.A.1
Draw points, lines, line segments, rays, angles (right, acute, obtuse), and perpendicular and parallel lines. Identify these in two-dimensional figures.
Matches standards in 50 statesSee each state's code
- Alabama MA19.4.24, MA19.4.27
- Alaska 4.MD.7.a, 4.MD.7.b, 4.G.1
- Arizona 4.MD.C.5.a, 4.MD.C.5.b, 4.G.A.1
- Arkansas 4.GM.1, 3.GM.2, 4.GM.4
- California 4.MD.C.5, 4.G.A.1
- Colorado 4.MD.C.5.a, 4.MD.C.5.b, 4.G.A.1
- Connecticut 4.MD.C.5, 4.G.A.1
- Delaware 4.MD.C.5, 4.G.A.1
- District of Columbia 4.MD.C.5, 4.G.A.1
- Florida MA.4.GR.1.1
- Georgia 4.GSR.7.1, 4.GSR.7.2, 3.GSR.6.1, 4.GSR.8.1
- Hawaii 4.MD.C.5, 4.G.A.1
- Idaho 4.MD.C.5.a, 4.MD.C.5.b, 4.G.A.1
- Illinois 4.MD.C.5, 4.G.A.1
- Indiana 3.G.2
- Iowa 4.MD.C.5.a, 4.MD.C.5.b, 4.G.A.1
- Kansas 4.G.2, 4.G.1
- Kentucky KY.4.MD.5, KY.4.G.1
- Louisiana 4.MD.C.5.a, 4.MD.C.5.b, 4.MD.C.5.c, 4.G.A.1
- Maine 4.MD.C.5a, 4.MD.C.5b, 4.G.A.1
- Maryland 4.GR.B.5, 4.GR.C.8
- Massachusetts 4.MD.C.5.a, 4.MD.C.5.b, 4.G.A.1
- Michigan 4.MD.C.5, 4.G.A.1
- Minnesota 4.3.2.2, 3.3.1.1
- Mississippi 4.MD.5.a, 4.MD.5.b, 4.G.1
- Missouri 4.GM.B.4, 4.GM.A.1
- Montana MT.4.MD.5.a, MT.4.MD.5.b, 4.D2.1, 4.D3.5, 4.D4.2, MT.4.G.1, 4.D2.2
- Nebraska 4.G.1.b, 4.G.2.d, 1.G.1.c, 4.G.1.a
- Nevada 4.MD.C.5, 4.G.A.1
- New Hampshire 4.MD.C.5, 4.G.A.1
- New Jersey 4.M.B.4a, 4.M.B.4b, 4.G.A.1
- New Mexico 4.MD.C.5, 4.G.A.1
- New York NY-4.MD.5.a, NY-4.MD.5.b, NY-4.G.1
- North Carolina NC.4.MD.6.a, NC.4.G.1
- North Dakota 3.GM.G.1, 4.GM.G.1
- Ohio 4.MD.5.a, 4.MD.5.b, 4.G.1
- Oklahoma 2.GM.1.5, 3.GM.1.3, 4.GM.1.1
- Oregon 4.GM.C.7, 4.GM.A.1
- Pennsylvania CC.2.4.4.A.6, CC.2.3.4.A.1
- Rhode Island 4.MD.C.5.a, 4.MD.C.5.b, 4.G.A.1
- South Carolina 3.MGSR.3.1
- South Dakota 4.MD.C.5.a, 4.MD.C.5.b, 4.G.A.1
- Tennessee 4.MD.C.5.a, 4.MD.C.5.b, 4.G.A.2, 4.G.A.1
- Texas 111.6.b.7.A, 111.6.b.7.B, 111.6.b.6.A
- Utah 4.MD.5.a, 4.MD.5.b, 4.G.1
- Vermont 4.MD.C.5, 4.G.A.1
- Virginia 1.MG.2e, 5.MG.3a, 4.MG.4a, 4.MG.4b, 4.MG.4c, 4.MG.4d, 4.MG.4e, 4.MG.5b, 4.MG.5f
- Washington 4.MD.C.5, 4.G.A.1
- West Virginia M.4.23, M.4.26
- Wisconsin M.4.MD.C.5, M.4.G.A.1