GeoBlog / 2006-07 / 2nd Period

 Formulas:

a²= b²+c²-2bc(cos<A)

b²= a²+c²-2ac(cos <B)

c²= a²+ b²-2ab(cos<C)

Use the law of Cosines when:

-you’re given three sides

-you’re given two sides and and <

Ex 1:

x=? y=11 z=25 <x= 45

x²=25²+11²-2(25)(11) cos 45

x²= 625-2(275) cos 45

x²= 625-550 (cos 45)

x= 18.9

Ex 2:

<L=?

24²=5²+27²-2(5)(27) cosL

576=25+729-770 (cosL)

178=270(cosL)

<L= 48.8