For all values of θ the locus of the point of intersection of the lines x cos θ+ y sin θ = a and x sin θ - y cos θ =b is
An ellipse
A circle
A parabola
A hyperbola
If x cos θ−y sin θ=a and x sinθ+y cosθ=b, then x2+y2a2+b2 = ___.