Browsing as Guest. Progress, bookmarks and attempts are disabled.
Log in to track your work.
June 2010 p31 q7
2010
The complex number 2 + 2i is denoted by u.
(i) Find the modulus and argument of u.
(ii) Sketch an Argand diagram showing the points representing the complex numbers 1, i and u. Shade the region whose points represent the complex numbers z which satisfy both the inequalities \(|z - 1| \leq |z - i|\) and \(|z - u| \leq 1\).
(iii) Using your diagram, calculate the value of \(|z|\) for the point in this region for which \(\arg z\) is least.
Solution
(i) The modulus of \(u = 2 + 2i\) is given by \(|u| = \sqrt{2^2 + 2^2} = \sqrt{8}\).
The argument of \(u\) is \(\arctan\left(\frac{2}{2}\right) = \frac{\pi}{4}\) or 45°.
(ii) On the Argand diagram, plot the points 1, i, and u. The perpendicular bisector of the line joining 1 and i is the line \(x = y\). The circle centered at \(u = 2 + 2i\) with radius 1 is drawn. The region satisfying \(|z - 1| \leq |z - i|\) is below the line \(x = y\), and the region satisfying \(|z - u| \leq 1\) is inside the circle. Shade the intersection of these regions.
(iii) The point in the shaded region for which \(\arg z\) is least lies on the tangent from the origin to the circle centered at \(u\). The distance from the origin to this tangent point is \(\sqrt{7}\).