If the angle between the lines joining the origin to the points of intersection of x + 2y + λ = 0 and 2x2 - 2xy + 3y2 + 2x - y - 1 = 0 is π/2, then a value of λ is:

Let PQR be a right-angled isosceles triangle, right-angled at Q(2, 1). If the equation of the line PR is 2x + y = 3, then the combined equation representing the pair of lines PQ and QR is:

One line of the pair of lines x2 + xy - 2y2 = 0 is perpendicular to one line of the pair of lines 3y2 - 5xy - 2x2 = 0. If the combined equation of the other two lines is ax2 + 2hxy + by2 = 0, then a + 2h + b =