Recall the area of a triangle formula

What this is

A formula to be told and then rehearsed: Area of a triangle formula: A = ½bh. It is the symbols version of Recall the area of a triangle (“The area of a triangle is half the base times the perpendicular height”). Teach the words first: the symbols come in the same order, so b is the base and h is the perpendicular height.

The routine

• Explain. Say the formula (“A equals a half b h”). Students repeat it.
• Frame. Say “Area of a triangle formula: A equals…”. Students give ½bh. Press Reveal to check.
• Reframe. The formula is turned around: ½bh is the formula for… Students give “the area of a triangle”.
• Rehearse. Nothing on screen. Students give the whole thing, label and formula.

Run it out loud first (individuals, then the whole class), then again on mini-whiteboards. You choose each time whether students say it or write it; the screen is the same either way. Reveal turns into Hide, so you can put the blank back and ask someone else.

Why it can simply be told

What A, b and h stand for comes from the words version, taught first. The rest is the algebra students already use: bh means b × h, and ½bh means half of it. The Reframe is there because ½bh is easily mixed up with the other area formulae; students should know whose formula it is, as well as what it is.