Let $z = 3+i$ and $w = 1-i$ - HSC - SSCE Mathematics Extension 2 - Question 2 - 2005 - Paper 1
Question 2
Let $z = 3+i$ and $w = 1-i$. Find, in the form $x + iy$,
(i) $2z + iw$,
(ii) $zw$,
(iii) $6/w$.
Let $\beta = 1 - i\sqrt{3}$.
(i) Express $\beta$ in mo... show full transcript
Worked Solution & Example Answer:Let $z = 3+i$ and $w = 1-i$ - HSC - SSCE Mathematics Extension 2 - Question 2 - 2005 - Paper 1
Step 1
Find, in the form x + iy, 2z + iw
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Answer
To solve for 2z+iw, first substitute the values of z and w:
2z=2(3+i)=6+2iiw=i(1−i)=i−1
Now, combine:
2z+iw=(6+2i)+(i−1)=5+3i.
Step 2
Find, in the form x + iy, zw
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Answer
To find the modulus of β:
∣β∣=12+(3)2=4=2.
For the argument, we have:
arg(β)=tan−1(−13)=−3π.
Thus, in modulus-argument form:
β=2cis(−3π).
Step 5
Express β³ in modulus-argument form
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Answer
Using the modulus and argument found:
β3=(2)3cis(3⋅−3π)=8cis(−π)=−8.
Step 6
Hence express β³ in the form x + iy
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Answer
The form x+iy derived from β3 is simply:
β3=−8+0i.
Step 7
Sketch the region on the Argand diagram
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Answer
To sketch the inequalities ∣z−z∣<2 and ∣z−1∣≥1:
The first inequality represents a region within a circle of radius 2 centered at z.
The second inequality represents the area outside or on the boundary of the circle of radius 1 centered at 1.
The intersection of these conditions should be marked distinctly on the Argand diagram.
Step 8
Explain why arg(z₁) + arg(z₂) = 2α
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Answer
When point P is reflected across the line l, the angle from the positive real axis to P plus the angle from the positive real axis to Q equals twice the angle of the line l, which is 2α. This is due to the nature of angle reflection in geometry.