I flipped open the cover when he gave the signal.
Twenty problems. Multiple choice for the first ten, free response for the last ten.
Find the derivative of f(x) = 3x² 5x - 7.
Easy. Power rule. Bring down the exponent, multiply, reduce the power by one.
6x 5.
Good. Next.
If f(x) = sin(2x), find f’(x).
Chain rule. The derivative of sin is cos, but you have to multiply by the derivative of the inside function.
2cos(2x).
Still with it. Next one.
Find the derivative of (x² 1)(3x - 4) using the product rule.
Product rule. First tis derivative of second, plus second tis derivative of first.
Except I couldn’t rember which was first and which was second.
Was it (x² 1) · 3 (3x - 4) · 2x?
Or was it backwards?
I stared at the problem.
The numbers didn’t move like Cassidy said hers did. They just sat there, mocking for not knowing sothing I’d done a hundred tis before.
Breathe.
Product rule is just distribution with extra steps. If you can’t rember the formula, derive it from first principles.
I worked through the algebra. Expanded everything. Combined like terms.
Got 9x² - 8x 3.
That felt right. Probably. Maybe.
I circled it and moved on.
The next seven problems blurred together. So I knew instantly. Others required to work backward from the answer choices, plugging in numbers until sothing clicked. By problem ten, my hand was cramping and I’d used the "when in doubt, pick C" strategy twice.
Not ideal.
The free response section was worse.
Find all critical points of f(x) = x³ - 6x² 9x 2.
Critical points ant taking the derivative and setting it equal to zero. Find where the slope was flat.
f’(x) = 3x² - 12x 9.
Set that equal to zero.
3x² - 12x 9 = 0.
Divide everything by 3.
x² - 4x 3 = 0.
Factor.
(x - 3)(x - 1) = 0.
So x = 3 or x = 1.
Good. That was right. I knew that was right.
Next problem.
A ladder 10 feet long leans against a wall. The bottom slides away from the wall at 2 feet per second. How fast is the top of the ladder sliding down when the bottom is 6 feet from the wall?
Related rates.
The problem I’d spent two hours teaching Harlow yesterday while she kept getting distracted by her phone buzzing with Fashion Club ergencies.
I set up the equation. Drew the triangle. Applied the Pythagorean theorem.
Then I forgot whether I was supposed to differentiate with respect to ti or with respect to x.
My pencil hovered.
I could picture Harlow’s face when she finally understood it. The way her eyes lit up and she said "OH!" so loud that Mrs. Chen shushed us from the reference desk.
I could picture Cassidy color-coding her graph paper in the library, tongue between her teeth as she concentrated.
I could picture Vivienne adjusting my collar with her fingers lingering just slightly too long.
I could picture Sabrina’s hand in my hair, her voice soft as she said sweet dreams.
What I couldn’t picture was the actual derivative of this related rates problem.
"Forty minutes remaining."
I was screwed.
Alright. New strategy. When you can’t rember the process, rember the principle.
Related rates ant everything changed together. The bottom moved, so the top moved. The rate of change connected them.
I worked through it slower. Step by step. Like I’d taught Cassidy.
Got an answer of -3/4 feet per second.
Negative because it was sliding down. That made sense.
I moved on to the next problem, and the next, and the next.
So I nailed. Others felt like I was guessing with extra steps.
By the ti Chen called ti, I had answers for everything. Whether those answers were correct remained a mystery I didn’t want to solve.
"Pass your tests forward."
I handed mine to the girl in front of .
Felix turned around again and made a throat-slitting gesture.
I gave him a thumbs up that I absolutely did not feel.
"Alright, get out of here. I’ll see you Monday."
The exodus was imdiate.
Felix grabbed my arm in the hallway. "Tacos. Now. I need to emotionally eat my feelings about that disaster, and you’re coming with ."
"I should—"
"No. Whatever you’re about to say, the answer is no. You look like you’re about to pass out. When’s the last ti you had a real lunch?"
I couldn’t actually rember.
"Exactly. Co on. My Range Rover has heated seats and good speakers. We’re getting al pastor and you’re gonna tell why you’ve been acting like soone replaced you with a sad robot."
"I don’t—"
"Nope. Already decided. Let’s go."
He pulled toward the parking lot before I could argue further.
His Range Rover sat in its usual spot, gleaming white and probably worth more than my entire apartnt building. Felix unlocked it with his key fob and climbed into the driver’s seat.
I got in the passenger side and imdiately sank into leather that probably cost more than my monthly rent.
"Buckle up. Chelsea is calling our nas."
He pulled out of the lot with the confidence of soone who’d never had to parallel park in his life, rging into traffic while simultaneously changing the radio station to sothing with way too much bass.
Manhattan passed by in its usual chaos. Taxis honking, delivery trucks double-parked, pedestrians jaywalking with the kind of death wish that ca from living here too long.
"Is it the Valentine sisters?" Felix asked. "Because you’ve been weird ever since you started working for them."
"Define weird."
"You check your phone every thirty seconds. You zone out during conversations. Yesterday you called Vivienne."
"I did not."
"You literally did. I said ’want chips?’ and you said ’not now, Vivienne, I’m thinking.’"
Oh.
That was bad.
"It’s just stress," I said. "The job’s demanding."
"Uh-huh. And I’m the next Emperor of Japan."
He turned onto a side street and pulled into a spot that definitely wasn’t legal but Felix had never cared about parking laws in his entire life.
"We’re here. Taqueria Guadalupe. Best al pastor in the city. My dad took here after I failed my driver’s test the first ti."
"You failed your driver’s test?"
"Twice. Don’t judge." He cut the engine. "Co on. Tacos wait for no man."
The place was small. Maybe six tables total, with a counter in the back and a kitchen visible through a window. The sll hit imdiately. Roasted pork, fresh cilantro, li, corn tortillas.
My stomach reminded I’d skipped breakfast.
An older woman with graying hair and kind eyes greeted Felix by na. "Félix! ¿Cómo estás, mijo?"
"Bien, Señora Rosa! This is my friend Isaiah. He’s having a day."
She looked at with that specific maternal assessnt that saw right through everything. "Ay, pobrecito. Sit, sit. I’ll bring you sothing good."
We took a corner table.
Felix leaned back in his chair. "Okay. Real talk. What’s actually going on?"
I considered lying.
Then I considered that Felix had been my best friend for three years and had never once asked for anything in return.
"My mom texted ."
His eyebrows shot up. "Your mom. The one who—"
"Yeah."
"Holy shit. What’d she say?"
"That she’s been thinking about us. That she’s sorry. That she wants to explain."
"And you said?"
"Nothing. I blocked her number."
Felix processed this. "Damn."
"Yeah."
"How do you feel about it?"
"Like I want to throw my phone into the Hudson and never think about her again."
"That’s fair. Also probably expensive."
"Hence the blocking instead."
Señora Rosa appeared with two plates piled high with tacos. Al pastor, cilantro, onions, li wedges. Probably a week’s worth of sodium.
Looked perfect.
"Eat," she commanded. "You’re too skinny."
I picked up a taco and bit in.
The flavor exploded across my tongue. Savory pork, bright li, fresh cilantro. The kind of food that reminded you that life had good monts between all the garbage.
Felix was already two tacos deep. "So your mom. You gonna tell Iris?"
"She already knows. Figured it out this morning."
"Smart kid."
"Too smart. She asked if I was okay approximately seventeen tis."
"Were you?"
"No."
"Are you now?"
I considered the question while eating my second taco.
"Not really. But the tacos help."
"See? I told you. Universal cure." He grabbed another one from his plate. "What about the Valentines? They know?"
"Vivienne figured it out yesterday. Didn’t even have to tell her."
"That’s... kind of scary actually. How’d she know?"
"She said I looked like I was punishing myself. Which apparently is sothing she recognizes because she does it too."
Felix paused mid-bite. "Wait. Vivienne Valentine opened up to you? About personal stuff?"
"Kind of."
"Bro. That’s huge. She doesn’t talk to anyone. Like, anyone. The girl runs half the school and nobody knows a single real thing about her."
"She’s seventeen and managing a billion-dollar brand while maintaining a 4.0. Can’t bla her for being closed off."
"Except she opened up to you."
"It wasn’t—"
"Dude." Felix set down his taco and looked at seriously. "I know you think you’re just the help or whatever. But those girls don’t act like that around normal staff."
"Your point?"
"My point is you’re not just their assistant anymore. If you ever were."
I finished my third taco instead of responding.
Felix wasn’t wrong. I knew he wasn’t wrong.
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