Finding a missing side
Put the angle and known side into the correct ratio, then rearrange to get the unknown side.
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Analogy
Like a recipe with one missing ingredient: you use the other amounts to work it out.
Example
Opposite is needed, so use sinsin 30 = opposite / 10opposite = 10 x sin 30= 10 x 0.5 = 5
In practice
Ladder safety: knowing the angle and length tells you how high it reaches.
Practice
Flashcards
- Find the opposite side if the hypotenuse is 10 and the angle is 30.5. Opposite = 10 x sin 30 = 10 x 0.5.
Questions people ask
Why should your calculator be in degree mode?
Calculators can measure angles in degrees or radians. School questions use degrees. In the wrong mode, sin 30 gives a strange answer instead of 0.5. Check for a small D or DEG on the screen before you start. Test it by pressing sin 90: in degree mode the answer should be exactly 1.
What if the unknown side is on the bottom of the fraction?
Rearrange so the unknown is on top. For cos 40 = 7 / x, swap them to get x = 7 / cos 40. That is about 9.14. Another way is to multiply both sides by x first, then divide.