
22 problems graded by difficulty (★ easy, ★★ medium, ★★★ hard). Try first, without looking at the solutions!
1 Product rule on polynomials ★★★
Let \( f(x)=(x^2+1)(x^3-2x) \). Use the product rule to find \( f'(x) \), then check your answer by expanding first.
2 A first quotient ★★★
Let \( g(x)=\dfrac{x}{x+3} \). Find \( g'(x) \) and compute \( g'(1) \).
3 Power of a linear function ★★★
Differentiate \( h(x)=(4x-7)^5 \) and evaluate \( h'(2) \).
4 Trigonometric sum ★★★
Let \( y=3\sin x-2\cos x+\tan x \). Find \( y' \) and evaluate it at \( x=0 \).
5 Exponentials and logarithms ★★★
Differentiate \( f(x)=5e^x-4\ln x+2^x \) for \( x\gt 0 \), and give \( f'(1) \) as an exact value and to two decimal places.
6 Successive derivatives ★★★
For \( f(x)=x^4-3x^3+2x \), find \( f'(x) \), \( f''(x) \), \( f^{(3)}(x) \) and \( f^{(4)}(x) \), then compute \( f''(2) \).
7 Velocity and acceleration of a cart ★★★
A cart on a track has position \( s(t)=t^3-6t^2+9t \) feet after \( t \) seconds. Find its velocity and acceleration at \( t=4 \), and the times when it is momentarily at rest.
8 Product with a sine ★★★
Let \( f(x)=x^2\sin x \). Find \( f'(x) \) and the exact value of \( f'(\pi) \).
9 Where is the tangent horizontal? ★★★
Let \( y=\dfrac{e^x}{x^2+1} \). Show that \( y'=\dfrac{e^x(x-1)^2}{(x^2+1)^2} \) and find every point where the tangent line is horizontal.
10 Cosine of a quadratic ★★★
Differentiate \( y=\cos(3x^2+1) \). Evaluate \( y' \) at \( x=0 \) and at \( x=1 \) (calculator, radians, two decimals).
11 Logarithm of a quadratic ★★★
Let \( y=\ln(x^2+4x+5) \). Explain why the function is defined for every real \( x \), then find \( y' \) and the value of \( x \) where \( y'=0 \).
12 Tangent line to an exponential product ★★★
Let \( f(x)=x\,e^{-2x} \). (a) Find the equation of the tangent line at \( x=0 \). (b) Find the point where the tangent line is horizontal.
13 Implicit slope of a tilted curve ★★★
The point \( (2,1) \) lies on the curve \( x^2+xy+y^2=7 \). Verify this, then find \( \dfrac{dy}{dx} \) and the tangent line at that point.
14 Derivatives of x ln x ★★★
For \( x\gt 0 \) let \( f(x)=x\ln x \). Find \( f' \), \( f'' \) and \( f^{(3)} \), then compute \( f''(4) \) and \( f^{(3)}(2) \).
15 Find the mistakes ★★★
A student wrote: (i) \( \dfrac{d}{dx}(x^2e^x)=2x\,e^x \); (ii) \( \dfrac{d}{dx}\sin(4x)=\cos(4x) \). Explain each error and give the correct derivatives.
16 A variable exponent ★★★
For \( x\gt 0 \) let \( y=x^{\sin x} \). Use logarithmic differentiation to find \( y' \), then compute \( y'\!\left(\dfrac{\pi}{2}\right) \).
17 A long product and quotient ★★★
Let \( y=\dfrac{(x^2+1)^3(2x-1)^4}{(x+5)^2} \) for \( x\gt \tfrac12 \). Use logarithmic differentiation to write \( \dfrac{y'}{y} \), then compute \( y'(1) \).
18 Three layers ★★★
Let \( y=\sqrt{\sin(x^2)} \). Find \( y' \), and evaluate it at \( x=\sqrt{\pi/6} \).
19 Second derivative of a circle ★★★
For the circle \( x^2+y^2=25 \), we know \( y'=-\dfrac xy \). Differentiate again to show that \( y''=-\dfrac{25}{y^3} \), then evaluate at \( (3,4) \) and say what it tells you about the concavity.
20 Inflating balloon ★★★
A spherical balloon has volume \( V=\tfrac43\pi r^3 \) cubic inches. Its radius grows at \( 0.5 \) inch per second. How fast is the volume growing when \( r=6 \) inches? (One inch is 2.54 cm.)
21 Proving the tangent rule ★★★
Use the quotient rule on \( \tan x=\dfrac{\sin x}{\cos x} \) to prove that \( \dfrac{d}{dx}\tan x=\sec^2x \).
22 Product of three functions ★★★
Let \( y=x\,e^x\sin x \). Extend the product rule to three factors, find \( y' \), and evaluate it at \( x=\tfrac\pi2 \).
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