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Consider the three vectors $ar{a} = ar{OA}, ar{b} = ar{OB}$ and $ar{c} = ar{OC}$, where O is the origin and the points A, B and C are all different from each other and the origin - HSC - SSCE Mathematics Extension 2 - Question 15 - 2024 - Paper 1

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Question 15

Consider-the-three-vectors-$ar{a}-=-ar{OA},-ar{b}-=-ar{OB}$-and-$ar{c}-=-ar{OC}$,-where-O-is-the-origin-and-the-points-A,-B-and-C-are-all-different-from-each-other-and-the-origin-HSC-SSCE Mathematics Extension 2-Question 15-2024-Paper 1.png

Consider the three vectors $ar{a} = ar{OA}, ar{b} = ar{OB}$ and $ar{c} = ar{OC}$, where O is the origin and the points A, B and C are all different from each o... show full transcript

Worked Solution & Example Answer:Consider the three vectors $ar{a} = ar{OA}, ar{b} = ar{OB}$ and $ar{c} = ar{OC}$, where O is the origin and the points A, B and C are all different from each other and the origin - HSC - SSCE Mathematics Extension 2 - Question 15 - 2024 - Paper 1

Step 1

Show that M lies on the line passing through A and B.

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Answer

To show that M lies on the line AB, we can express points A and B in vector form. Let A be represented as ar{a} and B as ar{b}. The line through AB can be expressed parametrically as:

ar{L}(t) = (1 - t)ar{a} + tar{b}, ext{ where } t ext{ is a scalar.}

Since M is defined as ar{OM} = rac{1}{2}(ar{a} + ar{b}), we can find a value of t such that ar{L}(t) = M. This can be achieved by setting:

t = rac{1}{2} ext{ which gives } M ext{ as a point on line AB.}

Step 2

Show that G lies on the line passing through M and C.

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Answer

To establish that G lies on the line MC, we can write C as ar{c}. The vector representation of G is given by ar{OG} = rac{1}{3}(ar{a} + ar{c}). The line through points M and C can be expressed as:

ar{L}(s) = (1 - s)ar{M} + sar{C}.

To find if G lies on this line, we need an s value such that ar{L}(s) = rac{1}{3}(ar{a} + ar{c}). Upon solving, we can verify that this is indeed a point on line MC, thereby confirming that G lies on it.

Step 3

Using part (ii), show that \( \frac{1}{3}(x + y + z) \) is never a cube root of wxz.

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Answer

Given the complex numbers x, y, z with modulus 1, we can express their sum:

w=13(x+y+z)w = \frac{1}{3}(x + y + z)

Using the property that for complex numbers with modulus 1, the sum cannot yield a cube root. If ww was a cube root of wxz, then we would have:

w3=wxz|w|^3 = |wxz|

However, since w<1|w| < 1, we conclude that rac{1}{3}(x + y + z) can never equal a cube root of wxz.

Step 4

Show that \( (2n + 4)I_n = a(2n + 1)I_{n-1} \).

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Answer

To prove this relation, we start by integrating by parts, letting:

u=(xn+1) extand dv=(ax)12dx.u = (x^n + 1)\ ext{ and } \ dv = (a - x)^{\frac{1}{2}} dx.

We find:

du=nxn1dx extand v=23(ax)32.du = n x^{n-1} dx \ ext{ and } \ v = \frac{2}{3}(a - x)^{\frac{3}{2}}.

Applying integration by parts, we arrive at the required relation through algebraic manipulation leading to:

Informula. extThus,(2n+4)In=a(2n+1)In1.I_n formula.\ ext{ Thus, } (2n + 4)I_n = a(2n + 1)I_{n-1}.

Step 5

Show that \( v^2 = \frac{51}{4} - \frac{27}{x^2} \).

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Answer

Considering the net acceleration expression, we start with:

a=27gx3g.a = \frac{27g}{x^3} - g.

Using F=maF = ma where m is mass and initial conditions, we derive the velocity by integrating the acceleration to reflect:

v2=51427x2v^2 = \frac{51}{4} - \frac{27}{x^2}

as required.

Step 6

Find where the object next comes to rest, giving your answer correct to 1 decimal place.

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Answer

To find the stopping point, we need to solve:

v2=0v^2 = 0

Solving ( 0 = \frac{51}{4} - \frac{27}{x^2} ) leads to:

x=27451x = \sqrt{\frac{27 \cdot 4}{51}}

Calculating this gives the value, and rounding to 1 decimal place provides the location.

Step 7

Using a suitable substitution, find \( \int \frac{2x^2}{\sqrt{2x - x^2}} dx \).

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Answer

Let us implement the substitution u=2xx2u = 2x - x^2, giving us:

du=(22x)dxdu = (2 - 2x) dx

This allows us to rearrange the integrand, ultimately simplifying the integral towards:

f(u)du\int f(u) du

resulting in a solvable form. The correct evaluation leads us to the answer for the integral.

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