Trig 4-3

Trig 4-3

The Law Of Cosines

Multiple Choice

What Let $C=90\degree$ . What happens to the  $-2ab\cos C$  term in equation 3 of the Law of Cosines?

• It becomes  $-2ab$  since  $\cos90\degree=1$  

• it becomes  $+2ab$ since  $\cos90\degree=-1$  

• It becomes $0$  since  $\cos90\degree=0$  

• It becomes  $-ab$  since  $\cos90\degree=\frac{1}{2}$  

Multiple Choice

Quick Check
Solve the triangle with  $a=9,\ b=9$  and  $c=9$  

•  $A=30\degree,\ B=60\degree,\ C=90\degree$  

•  $A=60\degree,\ B=60\degree,\ C=60\degree$  

•  $A=45\degree,\ B=45\degree,\ C=90\degree$  

•  $A=75\degree,\ B=25\degree,\ C=100\degree$