Maths · Trigonometry. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.
Trigonometry links the sides and angles of a right-angled triangle. Name the sides from the angle you are using: the hypotenuse is opposite the right angle, the opposite side faces your angle, and the adjacent side is next to your angle.
Choose the ratio that contains the side you know and the side you want. To find a side, use sin, cos or tan. To find an angle, use the inverse key: sin−1, cos−1 or tan−1.
Angles of elevation and depression are both measured from the horizontal: elevation looks up, depression looks down. Bearings are measured clockwise from north and written with three figures. The shortest distance from a point to a line is the perpendicular distance.
When the unknown side is on the bottom of the ratio, students multiply when they should divide. For example cos 35° = 9 ÷ h gives h = 9 ÷ cos 35°, not 9 × cos 35°. Also check that the calculator is in degree mode.
Answer: 11.0 cm
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