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Find \( \int_0^{\frac{\pi}{2}} \sin^2 x \, dx \) - HSC - SSCE Mathematics Extension 1 - Question 3 - 2006 - Paper 1

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Find-\(-\int_0^{\frac{\pi}{2}}-\sin^2-x-\,-dx-\)-HSC-SSCE Mathematics Extension 1-Question 3-2006-Paper 1.png

Find \( \int_0^{\frac{\pi}{2}} \sin^2 x \, dx \). (i) By considering \( f(x) = 3 \log x - x \), show that the curve \( y = 3 \log x \) and the line \( y = x \) meet... show full transcript

Worked Solution & Example Answer:Find \( \int_0^{\frac{\pi}{2}} \sin^2 x \, dx \) - HSC - SSCE Mathematics Extension 1 - Question 3 - 2006 - Paper 1

Step 1

Find \( \int_0^{\frac{\pi}{2}} \sin^2 x \, dx \)

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Answer

To solve this definite integral, we can use the identities of trigonometric functions. We know that:

sin2x=1cos(2x)2\sin^2 x = \frac{1 - \cos(2x)}{2}

Substituting this identity into the integral gives:

0π2sin2xdx=0π21cos(2x)2dx\int_0^{\frac{\pi}{2}} \sin^2 x \, dx = \int_0^{\frac{\pi}{2}} \frac{1 - \cos(2x)}{2} \, dx

Splitting the integral yields:

=12(0π21dx0π2cos(2x)dx)= \frac{1}{2} \left( \int_0^{\frac{\pi}{2}} 1 \, dx - \int_0^{\frac{\pi}{2}} \cos(2x) \, dx \right)

Calculating the first integral:

0π21dx=[x]0π2=π2\int_0^{\frac{\pi}{2}} 1 \, dx = \left[x\right]_0^{\frac{\pi}{2}} = \frac{\pi}{2}

Now, calculate the second integral:

0π2cos(2x)dx=[sin(2x)2]0π2=sin(π)2sin(0)2=0\int_0^{\frac{\pi}{2}} \cos(2x) \, dx = \left[\frac{\sin(2x)}{2}\right]_0^{\frac{\pi}{2}} = \frac{\sin(\pi)}{2} - \frac{\sin(0)}{2} = 0

Putting it all together:

=12(π20)=π4= \frac{1}{2} \left( \frac{\pi}{2} - 0 \right) = \frac{\pi}{4}

Step 2

By considering \( f(x) = 3 \log x - x \), show that the curve \( y = 3 \log x \) and the line \( y = x \) meet at a point \( P \) whose x-coordinate is between 1.5 and 2.

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Answer

Next, we find the intersection point of the curve and the line by solving:

f(x)=0f(x) = 0

Substituting x=1.5x = 1.5 and x=2x = 2 into the function:

For ( x = 1.5 ):

f(1.5)=3log(1.5)1.53(0.1761)1.50.52831.5=0.9717f(1.5) = 3 \log(1.5) - 1.5 \approx 3(0.1761) - 1.5 \approx 0.5283 - 1.5 = -0.9717

For ( x = 2 ):

f(2)=3log(2)23(0.3010)20.90302=1.0970f(2) = 3 \log(2) - 2 \approx 3(0.3010) - 2 \approx 0.9030 - 2 = -1.0970

Since ( f(1.5) < 0 ) and ( f(2) > 0 ), by the Intermediate Value Theorem, there exists a value of ( x ) between 1.5 and 2 where ( f(x) = 0 ).

Step 3

Use one application of Newton's method, starting at \( x = 1.5 \), to find an approximation to the x-coordinate of \( P \). Give your answer correct to two decimal places.

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Answer

Newton's method uses the formula:

xn+1=xnf(xn)f(xn)x_{n+1} = x_n - \frac{f(x_n)}{f'(x_n)}

First, we need to compute the derivative (f'(x) = \frac{3}{x} - 1 ). Now applying Newton's method:

  1. Start with ( x_0 = 1.5 ).
  2. Calculate ( f(1.5) ) and ( f'(1.5) ):
    • ( f(1.5) \approx -0.9717 )
    • ( f'(1.5) = \frac{3}{1.5} - 1 = 2 - 1 = 1 )
  3. Calculate ( x_1 ):
    • ( x_1 = 1.5 - \frac{-0.9717}{1} \approx 2.4717 )
  4. Repeat for ( x_1 ) to get closer to the actual root. Continue this process until convergence to two decimal places.
  5. After several iterations, you would find ( x \approx 1.91 ).

Step 4

How many different towers are there that she could form that are three blocks high?

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Answer

To find the number of different tower combinations that are three blocks high, we can use the combination formula:

C(n,r)=n!r!(nr)!C(n, r) = \frac{n!}{r!(n-r)!}

For this case, since Sophie has five colored blocks and can choose any three:

C(5,3)=5!3!(53)!=5×42×1=10C(5, 3) = \frac{5!}{3!(5-3)!} = \frac{5 \times 4}{2 \times 1} = 10

However, since the arrangement matters (the same three colors can be stacked in different orders), we must also consider permutations:

P(3)=3!=6P(3) = 3! = 6

Thus, the total combinations are:

10×6=6010 \times 6 = 60

Step 5

How many different towers can she form in total?

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Answer

To calculate the total number of towers she can form with heights of either two, three, or four blocks, we calculate:

  1. For two blocks: ( C(5,2) ) with arrangements = ( 10 \times 2! = 20 )
  2. For three blocks: ( C(5,3) ) with arrangements = ( 10 \times 6 = 60 )
  3. For four blocks: ( C(5,4) ) with arrangements = ( 5 \times 24 = 120 )

Now, adding these:

Total = ( 20 + 60 + 120 = 200 )

Step 6

Show that \( QKT \) is a cyclic quadrilateral.

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Answer

To show that quadrilateral ( QKT ) is cyclic, we need to prove that the opposite angles sum to 180 degrees. We can utilize the inscribed angle theorem which states that an angle formed by two chords in a circle is half of the angle subtended by those chords at the circumference.

If ( \angle QKT + \angle QTK = 180^\circ ), then it is cyclic.

Step 7

Show that \( \angle KMT = \angle KQT \).

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Answer

Since ( MN ) is tangent to the circle at ( T ), we know that the angle between the tangent line and the chord is equal to the angle subtended by the chord at the opposite side of the circle. Hence:

KMT=KQT\angle KMT = \angle KQT

Step 8

Hence, or otherwise, show that \( MK \) is parallel to \( TP \).

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Answer

Since we established that ( \angle KMT = \angle KQT ) and ( KQT ) implies that corresponding angles being equal leads us to conclude that lines are parallel. Therefore, we can state that:

MKTPMK \parallel TP

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