Answer:
[tex]c=11.8\ units[/tex]
Step-by-step explanation:
we know that
The formula of law of cosines is equal to
[tex]c^2=a^2+b^2-2(a)(b)cos(C)[/tex]
where
a, b and c are sides. C is the angle opposite side c
In this problem we have
[tex]a=3\ units\\b=10\ units[/tex]
[tex]C=120^o[/tex]
substitute the given values
[tex]c^2=3^2+10^2-2(3)(10)cos(120^o)[/tex]
[tex]c^2=109-(60)cos(120^o)[/tex]
[tex]c^2=109-(60)(-0.5))[/tex]
[tex]c^2=109+30[/tex]
[tex]c^2=139[/tex]
[tex]c=11.8\ units[/tex]
