AP Calculus BC 2016 FRQ: The Problems That Still Trip Students Up

AP Calculus BC 2016 FRQ: The Problems That Still Trip Students Up

If you've spent any time scouring the College Board archives, you know that not all exam years are created equal. Some years are a breeze. Others? They feel like a personal attack. The AP Calculus BC 2016 FRQ set falls somewhere in that spicy middle ground where conceptual depth starts to outweigh raw calculation. Honestly, looking back at these problems almost a decade later, they remain some of the best examples of why "just memorizing formulas" is a recipe for disaster in AP Calc.

Students walked into that May morning expecting the usual suspects. They got them, but with a twist. We saw the classic polar area challenge, the inevitable Taylor series struggle, and a particularly nasty separation of variables problem. But it’s the way the College Board phrased the questions that really separates the 5s from the 3s.

The Polar Rollercoaster: Question 2

Question 2 is often where the wheels start to shake. We were given two curves: a circle $r = 1$ and a polar curve $r = 2 + \cos(\theta)$. You’d think finding the area of the region inside the polar curve but outside the circle would be straightforward. It wasn't.

Most kids lost points right at the start because they couldn't find the correct limits of integration. You have to set $1 = 2 + \cos(\theta)$, which leads you to $\cos(\theta) = -1$. That happens at $\pi$. If you didn't visualize the symmetry of the graph, your integral was doomed. The formula for polar area is $\frac{1}{2} \int_{\alpha}^{\beta} [r(\theta)]^2 d\theta$, but in 2016, the College Board wanted to see if you actually understood the geometry. You weren't just plugging numbers in; you were slicing a pie that had a weird, off-center hole in the middle.

I’ve talked to tutors who say their students still struggle with this specific 2016 problem because of the "rate of change of the distance" part. Part (b) asked for the rate at which the distance between the two curves is changing with respect to $\theta$ at $\theta = \frac{\pi}{3}$. It sounds complicated. It’s basically just a derivative. But in the heat of the exam, "distance" feels like it needs a new formula. It doesn't. It’s just $r_2 - r_1$.

Why Question 4 Is a Separation of Variables Masterclass

Then there’s Question 4. This is the differential equation problem involving a funnel. Yes, a funnel. The height of the liquid is $h$, and the volume $V$ is given by $V = \frac{1}{20}(3 + h^3)$.

The math here is actually quite beautiful, but it's unforgiving. You had to find $\frac{dh}{dt}$. To do that, you needed the chain rule to link $\frac{dV}{dt}$ and $\frac{dh}{dt}$. If you missed that link, the rest of the problem vanished. The scoring guidelines from 2016 show that the College Board gives massive weight to the "separation of variables" step in part (c). If you don't separate the variables, you get a zero for the entire section. No partial credit. Nothing. It’s brutal.

$$\frac{dh}{dt} = -\frac{1}{10} \sqrt{h}$$

To solve this, you have to get all the $h$ terms on one side and the $t$ terms on the other.
$\int h^{-1/2} dh = \int -\frac{1}{10} dt$.
It looks simple on a whiteboard. It feels like climbing Everest when the clock is ticking and you've got three other problems looming in your mind.

The Taylor Series Trap in Question 6

We have to talk about the Taylor series. We have to. It’s Question 6, the traditional "final boss" of the BC exam. In 2016, they gave us a function $f$ with a Taylor series centered at $x = 1$.

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The first few parts were standard: find the interval of convergence. You use the Ratio Test. You check the endpoints. Standard stuff. But then came part (d). They introduced a new function $g$ and asked for the first three non-zero terms of the Taylor series for $g'$ (the derivative) centered at $x = 1$.

This is where the high-performers pull away. You don't rebuild the series from scratch. You differentiate the existing series term by term. If you understand that a Taylor series is just a "long polynomial," this is easy. If you view it as a mystical sequence of symbols, you’re stuck. The 2016 FRQ was testing your comfort level with the behavior of power series, not just your ability to run the Ratio Test like a calculator.

Funnel Trouble and the Mean Value Theorem

Question 5 was the "table problem." Everyone loves the table problems until they actually have to explain their reasoning. They gave us the velocity of a particle, $v_p(t)$, in a table.

One part asked if there's a time $t$ where the acceleration is zero. This is a classic Mean Value Theorem (MVT) or Rolle's Theorem setup. But here’s the kicker: you can’t just say "MVT says yes." You have to explicitly state that the function is differentiable and continuous on the interval. In 2016, hundreds of students lost a "point of communication" simply because they didn't write the word "continuous."

It feels pedantic. It kind of is. But in the world of AP Calculus, if you don't prove the prerequisites, the conclusion doesn't count.

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Common Mistakes on the 2016 Exam

  • Forgetting the constant of integration (+C): In the funnel problem, forgetting $+C$ meant you couldn't solve for the initial condition, costing at least 3 points.
  • Endpoint neglect: When finding the interval of convergence in Question 6, many forgot to actually plug the endpoints back into the series to see if they converged.
  • Misinterpreting "Rate of Change": Thinking $\frac{dr}{d\theta}$ was the same as $\frac{dy}{dx}$.
  • Units of Measure: Question 1 (the water tank) required units like "liters per hour." Missing these is a silly way to lose a point.

Is the 2016 FRQ Still Relevant?

Absolutely. If anything, the AP exam has moved even further toward the "conceptual explanation" style of the AP Calculus BC 2016 FRQ. They want to know if you can interpret the meaning of a definite integral in the context of a problem. In Question 1, for example, you had to explain what $\frac{1}{8} \int_{0}^{8} R(t) dt$ meant. It’s the average rate at which water is pumped into the tank over 8 hours.

If you just said "it's the average of R," you got nothing. You need context. You need time frames. You need units.

How to Practice These Effectively

Don't just do the problems and check the answers. That’s passive.

First, grab the 2016 scoring guidelines. Look at the "Distinction" notes. See how they award points for "setup" versus "answer." Often, the final answer is only worth 1 point, while the setup—the part that shows you actually understand the math—is worth 2 or 3.

Second, time yourself. Question 1 and 2 allow a graphing calculator. Questions 3 through 6 do not. Many students waste time using the calculator for basic arithmetic in the first two problems, then run out of time for the heavy lifting in the non-calculator section.

Third, pay attention to the "Explain your reasoning" prompts. In 2016, these were everywhere. Practice writing one or two clear sentences that link the mathematical theorem (like MVT or the Intermediate Value Theorem) to the specific numbers in the problem.

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Moving Forward with Your Prep

If you can master the AP Calculus BC 2016 FRQ, you're in great shape for the current exam format. The themes—rates of change, accumulation, series convergence, and differential equations—are the pillars of the BC curriculum.

Your Next Steps:

  • Download the 2016 FRQ PDF from the College Board website.
  • Set a timer for 90 minutes and try to do all six problems in one sitting. No distractions.
  • Grade yourself harshly. If you didn't write "differentiable," don't give yourself the point.
  • Focus on Question 6. If you can get a 7, 8, or 9 on a Taylor series problem like this one, you’re likely headed for a 5 on the overall exam.

The 2016 exam isn't just a relic. It’s a blueprint. Use it to find your weak spots before the actual test day finds them for you.