® If a quantity y varies with another quantity x , satisfying some rule

® If a quantity y varies with another quantity x , satisfying some rule y f x then dy dx (or ′ ) represents the rate of change of y with respect to x and x x dy dx (or f x ′ ) represents the rate of change of y with respect to x at ® If two variables x and y are varying with respect to another variable t , i.e., if f t and y g t , then by Chain Rule dy dy dx dx = , if dx dt ≠