1. The problem statement, all variables and given/known data If you make the change of variables: x= ucos([tex]\theta[/tex])-vsin([tex]\theta[/tex]) y= usin([tex]\theta[/tex])+vcos([tex]\theta[/tex]) where the angle 0 [tex]\leq[/tex] [tex]\theta[/tex] <[tex]\pi/2[/tex] is chosen in order to eliminate the cross product term in: 4x2+8xy+6y2=30 What is the angle you would use? 2. Relevant equations 3. The attempt at a solution I have no idea. Would you find when the 8xy term (in terms of the new variables) is zero (solve for theta)?