YEAR 8 MATHEMATICS · 2A
Lesson 2 — Angle Relationships · Interactive teacher demonstration
I DO · First rule

Complementary angles

Drag the slider. What always stays the same?

Together they make a right angle.

Two angles inside a right angle add up to 90°.

35° + 55° = 90°
35°
All the angles inside a right angle total 90°.
15-minute mini lesson · I DO → WE DO → YOU DOKeyboard: 1–5 sections · R reveal · ←/→ move · F full screen
Teacher prompts and suggested timing
  1. 2 minutes — Complementary: Show 35°, hide the missing angle, ask “What makes a right angle?” Reveal 55°.
  2. 3 minutes — Supplementary: Slide an angle along a straight line. Ask “How can we tell which operation to use?”
  3. 3 minutes — Vertically opposite: Move crossing lines and show opposite angles always remain equal. Ask “Do adjacent angles stay equal too?”
  4. 3 minutes — Around a point: Vary two angles; students calculate the remaining sector. Explain 360° as a full revolution.
  5. 4 minutes — Quick check: Show the four independent questions. Students respond on mini-whiteboards, then reveal answers.

Aligned to Cambridge Essential Mathematics CORE Year 8, Section 2A and the worksheet on angle relationships. No login, tracking or internet connection is required to run this page once downloaded.