vector{a}=(3;4)
|vector{a}|=sqrt(3^2+4^2)=5
cos α=a_(x)/|vector{a}|=3/5=0,6
cos β =a_(y)/|vector{a}|=4/5=0,8
f `_(x)=(x^2+(cosx/ √y))`_(x)=2x-sin(x/√y) * (x/√y)`_(x)=
=2x-sin(x/√y) * (1/√y)=2x- (1/sqrt(y))*sin(x/√y)
f `_(y)=(x^2+(cosx/ √y))`_(y)=0 - sin(x/√y) * (x/√y)`_(y)=
=- x*sin(x/√y) * (y^(-1/2))`= (x*sin(x/sqrt(y))/(2√(y^3))
f `_(vector{a})=(2x- (1/sqrt(y))*sin(x/√y))*0,6 + (x*sin(x/sqrt(y))/(2√(y^3))*0,8;
f `_(vector{a})(0;1)= -0,6+0*0,8=-0,6