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جستجو

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جستجوهای پرتکرار

میتونی لایو بذاری!

a) The complex number $u$ is defined by $u = \frac{5}{{\alpha  + 2i}}$, where the constant $\alpha $ is real.

(i) Express $u$ in the form $x + iy$, where $x$ and $y$ are real.

(ii) Find the value of $\alpha $ for which arg $\left( u \right) = \frac{3}{4}\pi $, where $u$ denotes the complex conjugate of $u$.

b) On a sketch of an Argand diagram, shade the region whose points represent complex numbers $z$ which satisfy both the inequalities $\left| z \right| \lt 2$ and $\left| z \right| \lt \left| {z - 2 - 2i} \right|$.

پاسخ تشریحی :
نمایش پاسخ

a)(i) EITHER: Multiply numerator and denominator by $\alpha  - 2i$, or equivalent

Obtain final answer $\frac{{5\alpha }}{{{\alpha ^2} + 4}} - \frac{{10i}}{{{\alpha ^2} + 4}}$, or equivalent

OR: Obtain two equations in $x$ and $y$, solve for $x$ or for $y$

Obtain final answer $x = \frac{{5\alpha }}{{{\alpha ^2} + 4}}$ and $y = \frac{{10}}{{{\alpha ^2} + 4}}$, or equivalent

(ii) Either state $arg\left( u \right) =  - \frac{3}{4}\pi $, or express $u$ in terms of $\alpha $ (f.t. on $u$)

Use correct method to form an equation in $\alpha $, e.g. $5\alpha  =  - 10$

Obtain $\alpha  =  - 2$ correctly

b) Show a point representing $2 + 2i$ in relatively correct position in an Argand diagram

Show the circle with centre at the origin and radius 2

Show the perpendicular bisector of the line segment from the origin to the point representing $2 + 2i$

Shade the correct region

[SR: Give the first B1 and the B1√ for obtaining $y = 2 - x$, or equivalent, and sketching the attempt.]

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