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.
Harder questions mix Pythagoras’ theorem and trigonometry, in flat shapes and in solids such as cuboids and pyramids. The method is always the same: find a right-angled triangle that contains what you want, draw it flat on its own, and label what you know.
If the triangle has two known sides and you want the third, use Pythagoras. If an angle is known or wanted, use sin, cos or tan. Many questions need two triangles: the first gives a length that you then use in the second.
In a solid, the angle between a line and a plane is the angle between the line and the line directly below it in the plane.
In a solid, students use a triangle that is not really right-angled, or use an edge of the base where the diagonal of the base is needed. Sketch the triangle separately and mark its right angle before calculating.
Answer: 13.9 cm
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