KEYWORD: DRAW diagram → write equation → differentiate w.r.t. t → plug in
A ladder 10 ft long leans against a wall. The bottom slides away at \(2\) ft/s. How fast is the top sliding down when the bottom is \(6\) ft from the wall?
Q 05
Derivatives — Chain Rule Trap
KEYWORD: \(\frac{d}{dx}[f(g(x))]=f'(g(x))\cdot g'(x)\) — don't forget the inner derivative!
If \(f(x)=\sin^2(3x^2)\), then \(f'(x)=\)
§3 Integration
Q 06
Integration — u-substitution
KEYWORD: spot f(g(x))·g'(x) → let u=g(x), du=g'(x)dx
📖 Key Example
\(\int 2x\cos(x^2)\,dx\): let \(u=x^2\), \(du=2x\,dx\) → \(\int\cos u\,du=\sin u+C=\sin(x^2)+C\)
\(\cos x = 1-\frac{x^2}{2!}+\frac{x^4}{4!}-\cdots\) so \(\cos(x^2)=1-\frac{x^4}{2}+\frac{x^8}{24}-\cdots\)
The Maclaurin series for \(xe^{x^2}\) begins with:
Q 18
Series — Alternating Series Test
KEYWORD: AST: terms must decrease → 0; error ≤ first omitted term
The series \(\displaystyle\sum_{n=1}^{\infty}\dfrac{(-1)^{n+1}}{n}=1-\tfrac{1}{2}+\tfrac{1}{3}-\cdots\) converges by the Alternating Series Test. The error from using the first 4 terms is at most: