Let z0 be a root of the quadratic equation, x2 + x + 1 = 0, If z = 3 + 6iz$$_0^{81}$$ $$-$$ 3iz$$_0^{93}$$, then arg z is equal to :
JEE · Math · previous-year question
- A.$${\pi \over 4}$$correct
- B.$${\pi \over 6}$$
- C.$${\pi \over 3}$$
- D.0
Answer
A. $${\pi \over 4}$$
Explanation
1 + x + x2 = 0 x = $${{ - 1 \pm \sqrt {1 - 4} } \over 2} = {{ - 1 \pm i\sqrt 3 } \over 2}$$ z0 = w, w2 Now z = 3 + 6iz$$_0^{81}$$ $$-$$ 3iz$$_0^{93}$$ z = 3 + 6iw81 $$-$$ 3iw93 (w93 = w81 = 1) $$ \Rightarrow $$ z = 3 + 3i then arg(z) = tan$$-$$1$$\left( {{3 \over 3}} \right)$$ = tan$$-$$1 (1) = $${\pi \over 4}$$
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