## Week 17- Trigonometry

This week we learned how to do some trigonometry and refresh some ideas from last year.

Before you do anything put down the three diagrams:

Also write down Soh Cah Toa, which can also be $S\frac{y}{r} C\frac{x}{r} T\frac{y}{x}$

SINE LAW: Now when using sine law to find a side you must use this formula $\frac{sinA}{a}=\frac{sinB}{b}=\frac{sinC}{c}$ if you want to find an angle you just flip the fractions over.

Ex:

to find the angle you use the formula of $\frac{sinA}{a}=\frac{sinB}{b}$

then plug in the numbers

$\frac{sin50}{20}=\frac{sinB}{17}$

which finally gives you \$latex \angleB=41

COSINE LAW: When using Cosine law if you want to find the side you want to use the formula $a^2=b^2+c^2-2bcCOSA$ if you want to find the $\angle$ You must use the formula $COSA=\frac{b^2+c^2-a^2}{2bc}$

Ex:

To find f you use the given formula $a^2=b^2+c^2-2bcCOSA$

then plug in the numbers

$a^2=21.3^2+30^2-2(21.3)(30)cCOS74$ $\sqrt{a^2}=\sqrt{1001}$

finally you get the answer of a=31.6