DepEd MELC reviewer for Grade 9 Mathematics, Quarter 4. Study the rules, worked formulas, and exam hacks below.
1
The Six Trigonometric Ratios
SOH-CAH-TOA
sin = Opp/Hyp cos = Adj/Hyp tan = Opp/Adj
sin = Opp/Hyp cos = Adj/Hyp tan = Opp/Adj
๐ก Exam Hack
Remember SOH-CAH-TOA. csc, sec, cot are just the reciprocals of sin, cos, tan.
2
Special Angles
| Angle | sin | cos | tan |
|---|---|---|---|
| 30ยฐ | ยฝ | โ3/2 | โ3/3 |
| 45ยฐ | โ2/2 | โ2/2 | 1 |
| 60ยฐ | โ3/2 | ยฝ | โ3 |
3
Angles of Elevation and Depression
Elevation = looking up from horizontal; depression = looking down. They are equal (alternate angles).
โ ๏ธ Common Mistake
The angle of depression is measured from the HORIZONTAL line, not from the vertical.
4
Worked Example
In a right triangle, opposite = 5, hypotenuse = 10. Find the angle.
sin ฮธ = 5/10 = 0.5 โ ฮธ = 30ยฐ
Pick the ratio that uses the two sides you know.
๐ Quick Recap โ Master These
Before your test, make sure you can confidently do each of the following:
- Explain and apply The Six Trigonometric Ratios.
- Explain and apply Special Angles.
- Explain and apply Angles of Elevation and Depression.
- Explain and apply Worked Example.
Re-read any section above where you hesitate, then try the worked example again without looking.