Х+200=-20+ 200= 180,
х+280=-20+280=260,
40 - 100 %
x (девочки) – 35
х = 35*40/100=14
40-14 = 26 мальчиков
<span>z=arctg(x/y) </span>
<span>z'(x)=1/(1+x^2/y^2)=y^2/(y^2+x^2)y=y/(x^2+y^2) </span>
<span>z'(y)=-x/(1+x^2/y^2)y^2=-x/(y^2+x^2) </span>
<span>z"(x,x)=-2xy/(y^2+x^2)^2 </span>
<span>z"(x,y)=((y^2+x^2)-y*2y)/(y^2+x^2)^2=(x^2-y^2)/(x^2+y^2)^2 </span>
<span>z"(y,y)=2xy/(x^2+y^2)^2</span>
Tg45 = 1
sin45 = √2/2
tg45-√2sin45=1-√2*√2/2=1-2/2=1-1=0