The complex number satisfies
- (i)
Sketch clearly the locus of on an Argand diagram.
- (ii)
Find the range of values of .
- (iii)
Find maximum value of .
It won't just hand you the answer — it asks where you're stuck.How the checker works
Worked solution
3(i)
1. Identify the region defined by the first inequality.
The inequality can be rewritten as:
This represents the set of points inside and on the boundary of a solid circular disk with centre and radius .
2. Determine the geometric constraint imposed by the argument inequality.
Let . Then (modulo ).
For the condition to hold, the complex number must lie strictly in the lower half-plane.
This means corresponds to an angle in the third or fourth quadrant, which implies must lie in the second or fourth quadrant:
3. Combine both conditions to define the exact boundary of the locus.
For points in the disk , the imaginary part of ranges from to .
Since , the vector representing must point upwards, meaning its angle must lie in the upper half-plane, i.e., .
Intersecting this with the quadrants found in Step 2, must strictly be in the second quadrant:
This strictly requires the real part of to be negative:
Thus, the required region is the strict left half of the circular disk.
Sketch Description:
- Draw the real () and imaginary () axes.
- Identify the circle centred at with radius .
- Draw a dotted vertical line segment along between the points and .
- Draw a solid semi-circular arc passing through , , and , representing the left half of the circle.
- Shade the region enclosed by the dotted line segment and the solid arc.
- Label key coordinates: centre , and boundary points , , and .
3(ii)
1. Contextualise the locus of $z$ using the conditions from part (i).
From part (i), the condition represents a solid disk centred at with radius 2.
For any point in , , so naturally lies in the interval .
The argument condition implies:
This strictly limits to the second quadrant, meaning .
Thus, the locus of is the left-half of , excluding the vertical boundary .
2. Calculate the maximum possible value of $|z-8|$.
represents the distance from to the point .
The distance from to the centre is:
The maximum possible distance from to the full disk is .
The point achieving this maximum distance is directly opposite through :
Since , lies well inside our restricted locus. Thus, the maximum value of is exactly .
3. Determine the infimum (strict minimum limit) of $|z-8|$ constrained by the locus.
The minimum possible distance from to the full disk is , which would occur at:
Since , this unconstrained minimum is outside the locus.
For points restricted to the locus, the square of the distance to is .
Because , we have .
Additionally, for all points inside the disk , the minimum possible value for is .
As gets arbitrarily close to (the bottom-right limiting boundary of the locus), the distance approaches:
Because the boundary is strictly excluded, must be strictly greater than .
4. State the final range of values.
Combining the strict lower bound and the achieved maximum distance, the range of values is:
3(iii)
1. Identify that the maximum argument corresponds to the tangent from $z=8$ to the circular locus.
The locus of is a region within the circle . The expression represents the angle made by the vector from to a point in the locus with the positive real axis.
To maximise this angle, we must consider the tangent line from to the circle that gives the largest angle, touching the circle at a point .
2. Calculate the relevant angles in the right-angled triangle formed by the centre of the circle, the point $z=8$, and the point of tangency.
Let be the centre of the circle. In the right-angled , the distance from to is:
The radius of the circle is .
The angle between the line and the tangent line is given by:
3. Find the angle of the line $PC$ and combine it with $\angle CPT$ to find the maximum argument.
The angle of the vector from the positive real axis is:
To maximise the argument, the tangent must be rotated further counter-clockwise from relative to . Thus, we add to the angle of :
(Note: The point of tangency has , which strictly satisfies the locus condition .)
AI analysis — may contain mistakes.
Worked this one out on paper? Snap your steps and Gigle's AI math checker will circle the step where it went wrong.
More questions on this topic
- 1Solve the equation , giving your roots in the form , where and . Ske…
- 2One of the roots of the equation is …
- 3One of the roots of the equation is…
- 4Find, in a simplified form, the cartesian equation of the locus of the point P representing the complex number z where …
- 5在复平面内,复数对应的点位于 A. 第一象限 B. 第二象限 C. 第三象限 D. 第四象限