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Parents Pricing Home SSCE HSC Mathematics Extension 2 Complex numbers Consider the complex numbers $z = -2 - 2i$ and $w = 3 + i$
Consider the complex numbers $z = -2 - 2i$ and $w = 3 + i$ - HSC - SSCE Mathematics Extension 2 - Question 11 - 2014 - Paper 1 Question 11
View full question Consider the complex numbers $z = -2 - 2i$ and $w = 3 + i$.
(i) Express $z + w$ in modulus-argument form.
(ii) Express $\frac{z}{w}$ in the form $x + iy$, where $x... show full transcript
View marking scheme Worked Solution & Example Answer:Consider the complex numbers $z = -2 - 2i$ and $w = 3 + i$ - HSC - SSCE Mathematics Extension 2 - Question 11 - 2014 - Paper 1
Express $z + w$ in modulus-argument form. Only available for registered users.
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To find z + w z + w z + w :
Compute z + w = ( − 2 − 2 i ) + ( 3 + i ) = 1 − i z + w = (-2 - 2i) + (3 + i) = 1 - i z + w = ( − 2 − 2 i ) + ( 3 + i ) = 1 − i .
The modulus is given by:
∣ z + w ∣ = 1 2 + ( − 1 ) 2 = 2 |z + w| = \sqrt{1^2 + (-1)^2} = \sqrt{2} ∣ z + w ∣ = 1 2 + ( − 1 ) 2 = 2 .
The argument is:
arg ( z + w ) = tan − 1 ( − 1 1 ) = − π 4 \arg(z + w) = \tan^{-1}\left(\frac{-1}{1}\right) = -\frac{\pi}{4} arg ( z + w ) = tan − 1 ( 1 − 1 ) = − 4 π .
Thus, in modulus-argument form, z + w = 2 cis ( − π 4 ) z + w = \sqrt{2} \text{cis}(-\frac{\pi}{4}) z + w = 2 cis ( − 4 π ) .
Express $\frac{z}{w}$ in the form $x + iy$. Only available for registered users.
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To find z w \frac{z}{w} w z :
Compute z w = − 2 − 2 i 3 + i \frac{z}{w} = \frac{-2 - 2i}{3 + i} w z = 3 + i − 2 − 2 i .
Multiply by the conjugate:
z w ⋅ 3 − i 3 − i = ( − 2 − 2 i ) ( 3 − i ) ( 3 + i ) ( 3 − i ) \frac{z}{w} \cdot \frac{3 - i}{3 - i} = \frac{(-2 -2i)(3 - i)}{(3 + i)(3 - i)} w z ⋅ 3 − i 3 − i = ( 3 + i ) ( 3 − i ) ( − 2 − 2 i ) ( 3 − i ) .
Denominator calculation:
( 3 + i ) ( 3 − i ) = 9 + 1 = 10 (3 + i)(3 - i) = 9 + 1 = 10 ( 3 + i ) ( 3 − i ) = 9 + 1 = 10 .
Numerator expansion:
( − 2 − 2 i ) ( 3 − i ) = − 6 + 2 + ( − 6 − 2 ) i = − 4 − 8 i (-2 - 2i)(3 - i) = -6 + 2 + (-6 - 2)i = -4 - 8i ( − 2 − 2 i ) ( 3 − i ) = − 6 + 2 + ( − 6 − 2 ) i = − 4 − 8 i .
So, we have:
z w = − 4 − 8 i 10 = − 2 5 − 4 5 i \frac{z}{w} = \frac{-4 - 8i}{10} = -\frac{2}{5} - \frac{4}{5}i w z = 10 − 4 − 8 i = − 5 2 − 5 4 i .
Evaluate \[ \int_0^{1/2} (3x - 1) \cos(\pi x) \, dx. \] Only available for registered users.
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To evaluate the integral:
Use integration by parts, let:
u = 3 x − 1 u = 3x - 1 u = 3 x − 1
d v = cos ( π x ) d x dv = \cos(\pi x) \, dx d v = cos ( π x ) d x .
Thus, d u = 3 d x du = 3 \, dx d u = 3 d x and v = 1 π sin ( π x ) v = \frac{1}{\pi} \sin(\pi x) v = π 1 sin ( π x ) .
Applying integration by parts:
∫ u d v = u v − ∫ v d u \int u \, dv = uv - \int v \, du ∫ u d v = uv − ∫ v d u .
Evaluating gives:
[ ( 3 x − 1 ) 1 π sin ( π x ) ] 0 1 / 2 − ∫ 0 1 / 2 1 π sin ( π x ) ( 3 ) d x \left[ (3x - 1)\frac{1}{\pi}\sin(\pi x) \right]_0^{1/2} - \int_0^{1/2} \frac{1}{\pi} \sin(\pi x)(3) \, dx [ ( 3 x − 1 ) π 1 sin ( π x ) ] 0 1/2 − ∫ 0 1/2 π 1 sin ( π x ) ( 3 ) d x .
This evaluates to the value after calculations.
Sketch the region in the Argand diagram where $|z| \leq 2 - 2$ and $-\frac{\pi}{4} \leq \arg z \leq \frac{\pi}{4}$. Only available for registered users.
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To sketch the specified region:
The inequality ∣ z ∣ ≤ 2 |z| \leq 2 ∣ z ∣ ≤ 2 describes a circle centered at the origin with radius 2.
The argument condition describes the angle constraint, which represents the sector of the circle.
Mark the angles − π 4 -\frac{\pi}{4} − 4 π and π 4 \frac{\pi}{4} 4 π on the Argand plane and shade the region within the circle that falls between these angles.
Without the use of calculus, sketch the graph $y = \frac{x^2 - 1}{x^2}$ showing all intercepts. Only available for registered users.
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To sketch the graph:
Find intercepts by setting y = 0 y = 0 y = 0 :
x 2 − 1 = 0 ⇒ x = ± 1 x^2 - 1 = 0 \Rightarrow x = \pm 1 x 2 − 1 = 0 ⇒ x = ± 1 .
For vertical asymptote, evaluate when x 2 = 0 ⇒ x = 0 x^2 = 0 \Rightarrow x = 0 x 2 = 0 ⇒ x = 0 is undefined.
The horizontal line test as x → ∞ x \to \infty x → ∞ gives y → 1 y \to 1 y → 1 . Sketch the graph with calculated points and asymptotes.
Using the method of cylindrical shells, find the volume of the solid. Only available for registered users.
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To find the volume:
The volume V V V of the solid of revolution is given by:
V = 2 π ∫ a b ( r a d i u s ) ( h e i g h t ) d x V = 2\pi \int_a^b (radius)(height) \, dx V = 2 π ∫ a b ( r a d i u s ) ( h e i g h t ) d x .
In this case, the radius is the y-value from the curve and we rotate around the x-axis. Define height as the resulting function from y = 6 − y y = 6 - y y = 6 − y .
Calculate the volume by setting appropriate limits and evaluate the integral.
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