Question

найдите угол между векторами a {5;-2;7} и b {7; 5; 2 } помогите пооожжжж

Answer 1

$cosalpha=frac{x_{1}x_{2}+y_{1}y_{2}+z_{1}z_{2}}{sqrt{x_{1}^2+y_{1}^2+ z_{1}^2}*sqrt{x_{2}^2+y_{2}^2+z_{2}^2}}=frac{35+(-10)+14}{sqrt{25+4+49}*sqrt{49+25+4}}=frac{39}{sqrt{78}*sqrt{78}}= frac{39}{78}=$$0,5$