Question 1103870
Use the dot product.
{{{u*v=abs(u)abs(v)cos(theta)}}}
{{{abs(u)=sqrt((-9)^2+8^2)=sqrt(81+64)=sqrt(145)}}}
{{{abs(v)=sqrt(10^2+(-8)^2)=sqrt(100+64)=sqrt(164)}}}
{{{u*v=-9(10)+(8)(-8)=-90-64=-154}}}
So,
{{{cos(theta)=(-154)/sqrt(145*164)}}}
{{{cos(theta)=-154/sqrt(23780)}}}
{{{cos(theta)=-0.99865}}}
{{{theta=177.03}}}