trig rules including the sine and cosine rules

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  • Created by: pippa
  • Created on: 29-05-12 13:42

right angled triangles


for all right angled triangles you must use soh cah toa 

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soh rule

soh is opposite over hypotensue = sin

if you are trying to find sin rememeber to use the shift button and then the sin button to gain the angle

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cah rule

cos is adjacent over hypotunese = cos

if you are trying to get the angle rememeber to use the shift button then the cos button on your calculator 

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toa rule

tan is opposite over adjcent = tan

if you are trying to find the angle press shift then the tan button on your calculator

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the sine rule

use if :

you have 2 sides and 1 angle and trying to find an angle

you have 1 side and 2 angles and trying to find a side

the side opposite the angle is a matching pair


a over sinx = b over siny

subsitute in the numbers 

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the cosine rule

you will always have 3 sides and 1 angle when using the cosine rule but one of them will be your unknown

the equation to use is:

a(squared) = b(squared) + c(squared) - 2bccosA

the a and cosA must be opposite to each other.

sub in the numbers and if needed rearrange the equation.

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Jonathan Newman


no info

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