Question

4) найдите угол между векторами: a(1;9;3) и b(-2;4;5)

Answer 1

$a(1;9;3); ;; ; b(-2;4;5)\\cos alpha = frac{acdot b}{|a|cdot |b|} = frac{-2+36+15}{sqrt{1+81+9}cdot sqrt{4+16+25}} = frac{49}{sqrt{91}cdot sqrt{45}} = frac{49}{ sqrt{4095} } \\ alpha =arccos frac{49}{sqrt{4095}}$