# Formulas for Triangles

the formulas you need to know :)

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• Created by: Kelly:)
• Created on: 03-06-11 19:58

## Trigonometry

remember: (label the triangle opposite (angle), adjacent (angle) and hypotenuse.

SOH (sin) CAH (cos) TOA (tan)

Use the function multiplied by the angle equalling the length values (dividing) in the correct way eg.,

angle = 30•
opp = x
hyp = 5
so... use SOH

sin30 = x/5 so...
5sin30 = x

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## Other Formulas

lower case letters = lengths
UPPER CASE LETTERS = ANGLES

sine rule
a/sinA = b/sinB = c/sinC

cosine rule
a^2 = b^2 + c^2 - 2bc cosA (find length)
A = cos^-1 (b^2 + c^2 - a^2) / 2bc (find angle)

area of any triangle
1/2 * a * b * sinC

NB: these will be on the formula sheet in your exam paper.
NB: you may need to rearrange them to suit what you need, and dependent on the values you actually know.

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that is good information :)

i like the basic information :) thanks!

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you're welcome! glad it helped! :) x

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Some hand references to triangle (trig) formulae.

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Thank you for this, helped me sm x

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