straight lines

1.If y = x tan11?/24 and y = x tan 19?/24 represent two straight lines at right angles, prove that the angle between the axes is ?/4.
2.Prove that the equation to the straight line which passes through the point (h, k) and is perpendicular to the axis of x is
x + y cosω = h + k cosω.
3.From each corner of a parallelogram a perpendicular is drawn upon the diagonal which does not pass through that corner and these are produced to form another parallelogram, shew that its diagonals are perpendicular to the sides of the first parallelogram and that they both have the same centre.
4.If the straight line y = mx + c and y =m’x + c’ make equal angles with the axis of x and be not parallel to one another, prove that m+m’+2mm’cosω=0

All these are in oblique coordinate system.The axes being inclined at an angle ω.
might not be of syllabus.but try these.

Hello dear
sorry I don't have time right to write d solution.
SLLoney has a detail discussion on oblique coordinates.
It will be very helpful .
And ya oblique cs have been asked JEE several times.
Thank u.

hey, i just wanted few question to share.its not that i don't know.i kept this here in zero level as i allready said its not in syllabus of CBSE.
abt JEE. i don't think so they were asked. but thanks:)