3.x/(x+y)^2
5.3(2)(1)=6
17.dx=1/y, 
dy=-x/y^2
19.dx=-x/sqrt(9-x^2y^2)
dy=-y/sqrt(9-x^2y^2)
21.dx=sin(y)cos(x)
dy=sin(x)sin(y)
27.e^(r+s)=dx,dy
31.dx=-2xe^(-x-y^2)
dy=-2ye^(-x-y^2)
39.dL=(M-Lt)/M^2e^(-Lt/M)
dM=(L(Lt-M))/M^3e^(-Kt/M)
dt=-L^2/M^2e^(-Lt/M)
47.a.I(95,50)=74
b.dI/dt 1.66

3.5x+10y-14=f'(x,y)
5.8x-2y-13=f'(x,y)
7.2-5s+4r=z
13.a.-16+4x+12y=f(x,y)
b.f(2.01,1.02)=4.3
f(1.97,1.01)=4
15.change(f)=3.6
17.f(0.01,-.02)=.98
23.8.44
25.4.998
27.3.945

7.grad(h)=[yz^-3 xz^-3 -3xyz^-4]
11.d/dt(f(r(t)))|t=0=-3
13.d/dt(f(r(t)))|t=0=5cos(1)
19.d/dt(f(g(r)))|t=1=0
27.D_uf(1,0)=6/sqrt(13)
31.D_uf(3,2)=50/sqrt(13)
33.D_uf(P)=-e^5/3=49.47
37.f inc at P in direct(v)
39.D_uf(P)=sqrt(6)/2
41.[6 2 4]
43.[4/sqrt(17) 9/sqrt(17) -2/sqrt(17)]
-1([4/sqrt(17) 9/sqrt(17) -2/sqrt(17)])