Let for some real numbers $$\alpha$$ and $$\beta$$, $$a = \alpha - i\beta $$. If the system of equations $$4ix + (1 + i)y = 0$$ and $$8\left( {\cos {{2\pi } \over 3} + i\sin {{2\pi } \over 3}} \right)x + \overline a y = 0$$ has more than one solution, then $${\alpha \over \beta }$$ is equal to
JEE · Math · previous-year question
- A.$$ - 2\sqrt 3 $$
- B.$$2 - \sqrt 3 $$correct
- C.$$2 + \sqrt 3 $$
- D.$$ - 2 - \sqrt 3 $$
Answer
B. $$2 - \sqrt 3 $$
Explanation
Given $$a = \alpha - i\beta $$ and $$4ix + (1 + i)y = 0$$ ...... (i) $$8\left( {\cos {{2\pi } \over 3} + i\sin {{2\pi } \over 3}} \right)x + \overline a y = 0$$ .... (ii) By (i) $${x \over y} = {{ - (1 + i)} \over {4i}}$$ ...... (iii) By (ii) $${x \over y} = {{ - \overline a } \over {8\left( {{{ - 1} \over 2} + {{\sqrt 3 i} \over 2}} \right)}}$$ ..... (iv) Now by (iii) and (iv) $${{1 + i} \over {4i}} = {{\overline a } \over {4\left( { - 1 + \sqrt 3 i} \right)}}$$ $$ \Rightarrow \overline a = \left( {\sqrt 3 - 1} \right) + \left( {\sqrt 3 + 1} \right)i$$ $$ \Rightarrow \alpha + i\beta = \left( {\sqrt 3 - 1} \right) + \left( {\sqrt 3 + 1} \right)i$$ $$\therefore$$ $${\alpha \over \beta } = {{\sqrt 3 - 1} \over {\sqrt 3 + 1}} = 2 - \sqrt 3 $$
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