Aparticle moving along a hyperbola xy =8. as it reaches the point (4,2), the y-coordinate is decreasing at a rate of 3cm/s. how fast is the x-coordinate of the point changing at that instant.

increasing by 6 cm/s. Since you're looking for rate of change per instant, you need to get the first derivative of the function the point is moving along. d/dx [xy] = 8 d/dx [y]*x + y*d/dx[x] = 0 y'x + 1y = 0 y'x + y = 0 y'x = -y y' = -y/x So the slope of the function at (4,2) is y' = -2/4 y' = -1/2 The rate of X changing will be this equation that then is solved for X. So -1/2 = -3/X -X/2 = -3 X = 6 So at the moment the particle reaches (4,2) the value of the x-coordinate is increasing at a rate of 6 cm/s