The distance covered by a particle in t seconds is given by x = 3 + 8t $$-$$ 4t². After 1 second its velocity will be

If the rate of increase of the radius of a circle is 5 cm/sec., then the rate of increase of its area, when the radius is 20 cm, will be

Angle between y² = x and x² = y at the origin is

If the normal to the curve y = f(x) at the point (3, 4) makes an angle 3$$\pi$$/4 with the positive x-axis, then f'(3) is