No title

Assignment #4:
Example for plotting zero contours of two functions: For x1 in [-8,8], x2 in [-10,10] plot points where sin(x1-x2)+x1^3/20 = 0 with solid blue curves, plot points where cos(x1+x2)-x2^2/20 = 0 with dashed red curves:
```
[X1,X2] = meshgrid(-8:.2:8,-10:.2:10);
contour(X1,X2, sin(X1-X2) + X1.^3./20 ,[0 0],'b-');  hold on
contour(X1,X2, cos(X1+X2) - X2.^2./20 ,[0 0],'r--'); hold off
```
Note that you MUST use .* ./ .^ instead of * / ^ for element-wise arithmetic operations with the arrays X1 and X2.