20. Incorrect. The answer is false, not true. dTC/dQ = MC = 4Q + 5. We employ three derivative rules to solve for dTC/dQ.

a. Constant-Function Rule. The derivative of a constant function equals zero. Examples: If y = a, then dy/dx = 0. If f(Q) = 1,500; then df/dQ = 0.

b. Power-Function Rule. If y = axⁿ then dy/dx = nax^n-1. Examples: If y = 0.5x⁴, then = dy/dx = 4*0.5x³. If y = x^-3, the dy/dx = -3x^-2

c. Sum-Difference Rule. If y = f(x) + g(x), dy/dx = df/dx + dg/dx. Examples: d/dx(3x⁵ + 2x) = 15x⁴+ 2, d/dx (4x³ - 2x² -5) = 12x² - 4x, d/dx (ax² - bx + c) = ax - b