Junior Cycle · Trigonometry Lesson 4 of 6

JCHL Trigonometry 4: Sketching a Right Angled Triangle

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You’ll learn

  • If you are given sin, cos or tan as a fraction, you might need to SKETCH a right-angled triangle and label the two sides
  • Use Pythagoras to find the third side
  • Then write down the trig ratio you were asked for

Formula used

sin = O/H, cos = A/H, tan = O/A; then O² + A² = H² for the missing side

On page 16 of the log tables — read it off, don’t memorise.

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