33. Incorrect. The answer is true not false. To find the marginal utility of good x, differentiate U(x,y) with respect to x holding y constant: ¶(-x² + 200xy – y²)/¶x = U_x = -2x + 200y. To find the marginal utility of good y, differentiate U(x,y) with respect to y holding x constant: U_y = 200x –2y.