← Day 20
UNIT 7 / 8 · LESSON 4 / 4 · 24 MINUTES

Draw and label before using a formula

A correct formula applied to the wrong length still produces a wrong answer. Mark all givens on the diagram.

01 / THE METHOD

Make it repeatable

  1. Draw a simple figure if none is supplied.
  2. Label angles, lengths, and units.
  3. Choose the relevant relationship: angle sum, area, similarity, or Pythagorean theorem.
  4. Check whether the requested value is a side, area, or angle.
02 / WORKED EXAMPLE

Watch the method in action

In a triangle, one angle is 114°. Could another angle be 67°?
  1. Triangle angles sum to 180°.
  2. The other two angles must total 66°.
  3. So neither can be 67° or larger.

A possible second angle must be between 0° and 66°.

03 / QUICK CHECK

Try it yourself

Which other angle could occur?

04 / PRACTISE AND CHECK

Apply the method to real questions

Start with guided questions and feedback. Then take a fresh independent set without hints. Reach at least 80% on that set to record this lesson.

Pass the quick check above to unlock practice.