A curve is specified in polar coordinates (r, u) in the form r = f(). Show that the sectorial area bounded by the line

A curve is specified in polar coordinates (r, u) in the form r = f(θ). Show that the sectorial area bounded by the line θ = α, θ = β and the curve r = f (θ) (α ≤ θ ≤ β) is given by

Also show that the angle Φ between the tangent to the curve at any point P and the polar line OP is given by

[f(0)] de