Crossing is not perpendicular: 3rd grade math lesson

What this lesson shows

Fixes a mistake

Two lines can cross without a square corner.

The worked example

The lesson works this one step by step: line BC intersecting line DE, not perpendicular, line FG perpendicular to line HJ. Then your kid tries one like it on paper.

The steps

Crossing lines intersect
Test with a paper corner
It fits: perpendicular
It misses: just intersecting

Helping at home

Lay the corner of a sheet of paper where the lines cross, one edge along a line. If the other edge lies along the other line, they are perpendicular. If it misses, they only intersect.

If your kid gets stuck

Lay a paper corner where they cross.

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.

See how Lux works

Standards

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 MA19.4.27
Alaska 4.G.1
Arizona 4.G.A.1
Arkansas 3.GM.2, 4.GM.4
California 4.G.A.1
Colorado 4.G.A.1
Connecticut 4.G.A.1
Delaware 4.G.A.1
District of Columbia 4.G.A.1
Florida MA.3.GR.1.1
Georgia 3.GSR.6.1, 4.GSR.7.1, 4.GSR.8.1
Hawaii 4.G.A.1
Idaho 4.G.A.1
Illinois 4.G.A.1
Indiana 3.G.2
Iowa 4.G.A.1
Kansas 4.G.1
Kentucky KY.4.G.1
Louisiana 4.G.A.1
Maine 4.G.A.1
Maryland 4.GR.C.8
Massachusetts 4.G.A.1
Michigan 4.G.A.1
Minnesota 3.3.1.1, 4.3.2.2
Mississippi 4.G.1
Missouri 4.GM.A.1
Montana MT.4.G.1, 4.D2.2, 4.D4.2
Nebraska 1.G.1.c, 4.G.1.a, 4.G.1.b
Nevada 4.G.A.1
New Hampshire 4.G.A.1
New Jersey 4.G.A.1
New Mexico 4.G.A.1
New York NY-4.G.1
North Carolina NC.4.G.1
North Dakota 3.GM.G.1, 4.GM.G.1
Ohio 4.G.1
Oklahoma 2.GM.1.5, 3.GM.1.3, 4.GM.1.1
Oregon 4.GM.A.1
Pennsylvania CC.2.3.4.A.1
Rhode Island 4.G.A.1
South Carolina 3.MGSR.3.1, 3.MGSR.3.2
South Dakota 4.G.A.1
Tennessee 4.G.A.1
Texas 111.6.b.6.A
Utah 4.G.1
Vermont 4.G.A.1
Virginia 1.MG.2e, 4.MG.4a, 4.MG.4b, 4.MG.4c, 4.MG.4d, 4.MG.4e, 4.MG.5b, 4.MG.5f, 5.MG.3a
Washington 4.G.A.1
West Virginia M.4.26
Wisconsin M.4.G.A.1

Crossing is not perpendicular