STEP-BY-STEP ANSWER:
Step 1: Confirm the integrand is already in a form that matches the power rule; x^3 is equivalent to x^3.
Step 2: Apply the power rule: ∫x^n dx = x^(n+1)/(n+1) + C, for n ≠-1.
Step 3: Substitute n = 3 to get ∫x^3 dx = x^(3+1)/(3+1) + C = x^4/4 + C.
Final Answer: ∫ x^3 dx = x^4/4 + C.