[tex]IACI=\sqrt{(0-2)^2+(1-1)^2} =\sqrt{4}=2\\ IABI=\sqrt{(-3-2)^2+(2-1)^2}=\sqrt{26}\\ IBCI=\sqrt{(0-(-3))^2+(1-2)^2}=\sqrt{10}[/tex]
[tex]cosC=\frac{IACI^2+IBCI^2-IABI^2}{2IACI*IBCI}=\frac{4+10-26}{2*2*\sqrt{10} }=-\frac{12}{4\sqrt{10} }= -\frac{3}{\sqrt{10} }[/tex]
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[tex]IACI=\sqrt{(0-2)^2+(1-1)^2} =\sqrt{4}=2\\ IABI=\sqrt{(-3-2)^2+(2-1)^2}=\sqrt{26}\\ IBCI=\sqrt{(0-(-3))^2+(1-2)^2}=\sqrt{10}[/tex]
[tex]cosC=\frac{IACI^2+IBCI^2-IABI^2}{2IACI*IBCI}=\frac{4+10-26}{2*2*\sqrt{10} }=-\frac{12}{4\sqrt{10} }= -\frac{3}{\sqrt{10} }[/tex]