The points ($$-$$a, $$-$$b), (a, b), (0, 0) and (a², ab), a $$ \ne $$ 0, b $$ \ne $$ 0 are always

The locus of the point of intersection of the straight lines $${x \over a} + {y \over b} = K$$ and $${x \over a} - {y \over b} = {1 \over K}$$, where K is a non-zero real variable, is given by

A straight line joining the points (1, 1, 1) and (0, 0, 0) intersects the plane 2x + 2y + z = 10 at

Angle between the planes x + y + 2z = 6 and 2x $$-$$ y + z = 9 is