Finding Missing Sides

Method

1. Label Opp, Adj, Hyp for the given angle.
2. Choose sin, cos or tan depending on which two sides you have.
3. Solve.

Example: Right triangle, angle 35°, adjacent = 10 cm, find opposite.
Use tan: tan 35° = opp/10   ⇒   opp = 10 × tan 35° = 10 × 0.7002 = 7.00 cm (3 s.f.)

Example: Angle 50°, hypotenuse = 12 cm, find adjacent.
Use cos: cos 50° = adj/12   ⇒   adj = 12 × cos 50° = 12 × 0.6428 = 7.71 cm

Discussion

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