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# Calculus 3: midterm

1. Find all points on the curve $x=\cos3t,y=2\sin t$ where the tangent is either horizontal or vertical.
2. Determine whether these points lie on a straight line: $A(0,-5,5),B(1,-2,4),C(3,4,2).$
3. Sketch the parametric curve $x=\frac{1}{t}\cos t,y=\frac{1}{t}\sin t,t>0.$
4. Find the unit tangent vector of the curve $r(t)=t\mathbf{i}+t\mathbf{j}+(1+t^{2})\mathbf{k}$ at the point $<0,0,1>.$
5. Find the plane through the point $(-1,6,-5)$ and parallel to the vectors $a=<1,1,0>$ and $b=<0,1,1>.$
6. Show that the limit doesn't exist: $\lim_{(x,y)\rightarrow(0,0)}\frac{xy}{x^{2}+y^{2}}.$
7. Find the linearization of the function $f(x,y)=e^{xy}$ at $(0,1).$