What is the value of r if the distance between the point (4,2) and (1,r) is 3 units?

If y = 3 cos 4x, dy/dx equals?

Find the value of sin 45° - cos 30°

A cliff on the bank of a river is 300 meter high. if the angle of depression of a point on the opposite side of the river is 60º, find the width of the river?

If s = (2 + 3t)(5t - 4), find ds/dt when t = 4/5 secs