1. The problem asks how the integrand was obtained for parts 1, 2, and 3. 2. The integrand is the function inside the integral sign that we integrate with respect to a variable. 3. To find the integrand, we start from the problem's context or the function we want to integrate. 4. For example, if the problem involves finding the area under a curve $y=f(x)$, the integrand is simply $f(x)$. 5. If the problem involves a physical quantity like velocity or force, the integrand might be derived from formulas or expressions given. 6. In parts 1, 2, and 3, the integrand was obtained by identifying the function or expression that needs to be integrated based on the problem's setup. 7. This often involves rewriting the problem in terms of a variable and expressing the quantity to be summed or accumulated as a function of that variable. 8. Without the exact problem statement, the general rule is: the integrand is the function inside the integral that represents the quantity to be accumulated or summed. 9. If you provide the original problem or expressions, I can show exactly how the integrand was derived step-by-step.