[m]v_{cр}=\frac{S}{t}[/m]
[m] t=t_{1}+t_{2}+t{_3}[/m]
[m]t_{1}=\frac{\frac{1}{3}S}{60}[/m]
[m]t_{2}=\frac{\frac{1}{3}S}{120}[/m]
[m]t_{3}=\frac{\frac{1}{3}S}{40}[/m]
⇒
[m]v_{cр}=\frac{S}{\frac{\frac{1}{3}S}{60}+\frac{\frac{1}{3}S}{120}+\frac{\frac{1}{3}S}{40}}=\frac{120S}{\frac{2}{3}S+\frac{1}{3}S+S}=\frac{120S}{2S}=60[/m]
12.
x^2+4x+20=(x+2)^2+16
наименьшее значение при [b]x=-2[/b]