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Elementary Trigonometry

Theory Refresher

Click here for "Live" theory (64.2mb).

Trigonometry is all about angles and sides of a right-angled triangle.

Recall that the side of the triangle opposite the right-angle is called the hypotenuse (Hyp). Further, note in the diagram that side is opposite (Opp) angle and side is adjacent (Adj) to angle .

Trigonometric Ratios


Reciprocal Ratios


To find the exact value of these ratios for angles 30o, 45o and 60o, read the values from the following key triangles (for other values, use your calculator).

For 45o:
Isosceles right triangle,
side length 1
        For 30o and 60o:
Equilateral triangle,
side length 2

Solving problems

Trigonometric ratios can be used to solve problems involving right-angled triangles. In these cases, make sure you draw a diagram and label it carefully.

And do not forget about Pythagoras' Theorem:
(that is, "the square of the hypotenuse is equal to the sum of the squares of the other two sides.")

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