Recall the angles on a straight line fact

What this is

A fact to be told and then rehearsed: Angles on a straight line add up to 180°. It is the second step of finding a missing angle on a straight line. Students have already decided which angles are on a straight line; this fact says what those angles add up to. Writing the calculation comes next.

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 words on screen. Students finish the sentence.
• 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

Every idea in the fact is already secure or is plain English. “Angles on a straight line” comes from Are these angles on a straight line?, so teach that first: on its own, the phrase is easy to misread as “angles that touch a line”. “Add up to” is plain English. The only new thing is the number.

This is the first place in the routine where degrees appear, so check that students know angles are measured in degrees before you tell them the fact.

Where it comes from

A full turn is 360°. A straight line is half a turn, and half of 360° is 180°.