Recall the area of a triangle

What this is

A fact to be told and then rehearsed: The area of a triangle is half the base times the perpendicular height. It is the words version of the formula A = ½bh, and the words come in the same order as the symbols: half, base, height. Teach this one before the formula, so that b and h already mean something.

The routine

• Explain. Say the whole fact. Students repeat it.
• Frame. Say the first half. Students give the second half. Press Reveal to check.
• Reframe. The fact is turned around. Say the half on screen. Students give the other half.
• Rehearse. Nothing on screen. Students give the whole fact.

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

“Area” and “triangle” are already secure, and “half” and “times” are plain English. Check two words before you start: the base can be any side of the triangle, not just the one at the bottom, and the perpendicular height is the length at right angles to it, not a sloping side. Which two lengths tell the area of the triangle? practises picking them out on a diagram.