Question Bank

Official NZQA past exam questions • AS91578 Differentiation

With video explanations by infinityplusone

15 questions
Achievement
Differentiate y=2x3+5(x3+2)3y = 2x^3 + \dfrac{5}{(x^3 + 2)^3}

*You do not need to simplify your answer.*
Achievement
If f(x)=3cos3xf(x)=3\cos 3x, show that 9f(x)+f(x)=09f(x)+f''(x)=0.
Find the gradient of the curve y=lnsin2xy = \ln|\sin^2 x| at the point where x=π6x = \dfrac{\pi}{6}

You must use calculus and show any derivatives that you need to find when solving this
problem.
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A car is being pulled along by a rope attached to the tow-bar at the back of the car.

The rope passes through a pulley, the top of which is 3 m further from the ground than the tow-bar.

The pulley is xx m horizontally from the tow-bar, as shown in the diagram above.

The rope is being winched in at a speed of 0.60.6 m s1^{-1}.

The wheels of the car remain in contact with the ground.

At what speed is the car moving when the length of the rope, LL, between the tow-bar and the pulley is 5.45.4 m?

*You must use calculus and show any derivatives that you need to find when solving this problem.*
Excellence
A curve is defined by the parametric equations

x=t3+1x = t^3 + 1
y=t2+1y = t^2 + 1

Show that d2ydx2(dydx)4\dfrac{\dfrac{d^2y}{dx^2}}{\left(\dfrac{dy}{dx}\right)^4} is a constant.
Achievement
Differentiate y=3x+cosec5x.y = 3\sqrt{x} + \mathrm{cosec}\,5x.
Achievement
A particle is travelling in a straight line. The distance, in metres, travelled by the particle may
be modelled by the function

s(t)=ln(3t2+3t+1)s(t)=\ln(3t^2+3t+1)

t0t\geq 0

where tt is time measured in seconds.

Find the velocity of this particle after 2 seconds.

*You must use calculus and show any derivatives that you need to find when solving this
problem.*
The diagram below shows the graph of the function y=f(x)y = f(x).
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For the function above:

(i) What is the value of f(1)f(1)?
State clearly if the value does not exist.

(ii) For what value(s) of xx does the function f(x)f(x) not have a limit?

(iii) Find all the value(s) of xx that meet the following conditions:

(1) f(x)>0f'(x) > 0:

(2) f(x)=0f'(x) = 0 and f(x)<0f''(x) < 0:

(3) f(x)f(x) is continuous but not differentiable:
If y=ex(2x2x1)y = e^x(2x^2 - x - 1), find the value(s) of xx for which dydx=0\dfrac{dy}{dx} = 0.

You must use calculus and show any derivatives that you need to find when solving this
problem.
Excellence
A water tank is in the shape of an inverted right-circular cone.

The height of the cone is 200 cm and the radius of the cone is 80 cm.
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The tank is being filled with water at a rate of 150 cm3150\ \mathrm{cm}^3 per second.

At what rate will the surface area of the water in the tank be increasing when the depth of
water in the tank is 125 cm?

*You must use calculus and show any derivatives that you need to find when solving this
problem.*
Achievement
Differentiate y=e2xx2+1y = \dfrac{e^{2x}}{x^2 + 1}.

You do not need to simplify your answer.
Achievement
A curve is defined parametrically by the parametric equations

x=5e2tx = 5e^{2t}

y=2e5ty = 2e^{5t}

Find the gradient of the tangent to this curve at the point where t=0t = 0.
*You must use calculus and show any derivatives that you need to find when solving this problem.*