Question 1086197
Use the dot product,
{{{AB}}}=({{{1-7}}},{{{7-4}}})=({{{-6}}},{{{3}}})
{{{AC}}}=({{{-3-7}}},{{{-4-4}}})=({{{-10}}},{{{-8}}})
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{{{cos(A)=(AB*AC)/(abs(AB)abs(AC))}}}
{{{cos(A)=(-6(-10)+3(-8))/(sqrt((-6)^2+(3)^2)sqrt((-10)^2+(-8)^2))}}}
{{{cos(A)=(36)/(sqrt(45)sqrt(164))}}}
{{{cos(A)=(6sqrt(205))/205}}}
{{{A=65.2}}}