What is acute angle ?

What is the acute angle between the lines Ax+By=A+B and A( x-y)+B(x+y)=2B ?

What is the acute angle between the planes x+y+2z=3 and -2x+y-z=11 ?

What is the acute angle between the curves xy=2 and y^2=4x at their point of intersection ?

What is the acute angle between the lines x-2=0 and sqrt3x-y-2=0 ?

A line make angle 60^(@) and 45^(@) with the positive direction of x-axis and y-axis repectively. What acute angle does it make with the z-axis?

What is the acute angle between the lines represent by the equation y-sqrt(3x)-5 =0 and sqrt(3y) -x +6=0 ?