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The derivative of a function f(x) is given by $$f'(x) = ext{sin} \, x.$$ Find f(0), given that f(0) = 2 - HSC - SSCE Mathematics Extension 1 - Question 2 - 2010 - Paper 1

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The-derivative-of-a-function--f(x)--is-given-by--$$f'(x)-=--ext{sin}-\,-x.$$---Find--f(0),-given-that--f(0)-=-2-HSC-SSCE Mathematics Extension 1-Question 2-2010-Paper 1.png

The derivative of a function f(x) is given by $$f'(x) = ext{sin} \, x.$$ Find f(0), given that f(0) = 2. (b) The mass M of a whale is modelled by $$M ... show full transcript

Worked Solution & Example Answer:The derivative of a function f(x) is given by $$f'(x) = ext{sin} \, x.$$ Find f(0), given that f(0) = 2 - HSC - SSCE Mathematics Extension 1 - Question 2 - 2010 - Paper 1

Step 1

Find f(0)

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Answer

To find ( f(0) ), we can integrate the given derivative function. The integral of ( \text{sin} , x ) is ( -\text{cos} , x + C ). Thus, we have:

f(x)=cosx+Cf(x) = -\text{cos} \, x + C

Using the condition ( f(0) = 2 ):

f(0)=cos0+C=1+C=2C=3,f(0) = -\text{cos} \, 0 + C = -1 + C = 2 \Rightarrow C = 3,

therefore,

f(x)=cosx+3.f(x) = -\text{cos} \, x + 3.

Step 2

Show that the rate of growth of the mass of the whale is given by the differential equation

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Answer

To derive the differential equation, we differentiate the mass model:

M=3635.5ektM = 36 - 35.5e^{-kt}

Differentiating with respect to ( t ):

dMdt=0(35.5)(k)ekt=k(35.5)ekt.\frac{dM}{dt} = 0 - (35.5)(-k)e^{-kt} = k(35.5)e^{-kt}.

Now recognizing that ( M ) approaches 36 as ( t ) increases, we rewrite the above as:

dMdt=k(36M).\frac{dM}{dt} = k(36 - M).

Step 3

When the whale is 10 years old, its mass is 20 tonnes. Find the value of k, correct to three decimal places.

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Answer

At ( t = 10 ), ( M = 20 ) tonnes:

Using the mass model:

20=3635.5e10k35.5e10k=16e10k=1635.5.20 = 36 - 35.5e^{-10k} \Rightarrow 35.5e^{-10k} = 16 \Rightarrow e^{-10k} = \frac{16}{35.5}.

Taking the natural logarithm:

10k=ln(1635.5)k=110ln(1635.5).-10k = \ln\left(\frac{16}{35.5}\right) \Rightarrow k = -\frac{1}{10} \ln\left(\frac{16}{35.5}\right).

Calculating this gives:

k0.0706943,k \approx 0.0706943, which rounds to 0.071.

Step 4

According to this model, what is the limiting mass of the whale?

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Answer

The limiting mass occurs when ( t \to \infty ). As ( t \to \infty ):

M3635.5ekt3635.50=36.M \to 36 - 35.5e^{-kt} \to 36 - 35.5 \cdot 0 = 36.

Thus, the limiting mass of the whale is 36 tonnes.

Step 5

Find the values of a and b.

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Answer

Since ( x - 3 ) is a factor, ( P(3) = 0 ):

P(3)=(3+1)(33)Q(3)+3a+b=03a+b=0.\label1P(3) = (3+1)(3-3)Q(3) + 3a + b = 0 \Rightarrow 3a + b = 0.\label{1}

Using the remainder, when dividing by ( x + 1 ):

P(1)=0+(13)Q(1)+(a+b)=84Q(1)a+b=8.\label2P(-1) = 0 + (-1 - 3)Q(-1) + (-a + b) = 8 \Rightarrow -4Q(-1) -a + b = 8.\label{2}

Solving equations ({1}, {2} ), we find the values of ( a ) and ( b ).

Step 6

Find the remainder when P(x) is divided by (x + 1)(x - 3).

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Answer

Use polynomial long division or synthetic division. When ( P(x) ) is divided by ( (x + 1)(x - 3) ), find the resulting remainder, which can be expressed in the form:

R(x)=Ax+BR(x) = Ax + B

Use the previously obtained values for ( a ) and ( b ) to determine the specific remainder.

Step 7

Find an expression in terms of x for \( \frac{dr}{dt} \) where t is time in hours.

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Answer

By applying the Pythagorean theorem:

M2=S2+r236=x2+r2.M^2 = S^2 + r^2 \Rightarrow 36 = x^2 + r^2.

Differentiate with respect to t:

0=2xdxdt+2rdrdtdrdt=xrdxdt.0 = 2x\frac{dx}{dt} + 2r\frac{dr}{dt} \Rightarrow \frac{dr}{dt} = -\frac{x}{r}\frac{dx}{dt}.

Given ( \frac{dx}{dt} = 100 ) km/h, substitute to find ( \frac{dr}{dt}. $$

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