1
WB JEE 2018
MCQ (Single Correct Answer)
+2
-0.5
Change Language
Let $$\overrightarrow \alpha $$, $${\overrightarrow \beta }$$, $${\overrightarrow \gamma }$$ be the three unit vectors such that $$\overrightarrow \alpha .\overrightarrow \beta = \overrightarrow \alpha .\overrightarrow \gamma = 0$$ and the angle between $$\overrightarrow \beta $$ and $$\overrightarrow \gamma $$ is 30$$^\circ$$. Then $$\overrightarrow \alpha $$ is
A
2($$\overrightarrow \beta $$ $$ \times $$ $$\overrightarrow \gamma $$)
B
$$-$$ 2($$\overrightarrow \beta $$ $$ \times $$ $$\overrightarrow \gamma $$)
C
$$ \pm $$ 2($$\overrightarrow \beta $$ $$ \times $$ $$\overrightarrow \gamma $$)
D
($$\overrightarrow \beta $$ $$ \times $$ $$\overrightarrow \gamma $$)
2
WB JEE 2018
MCQ (Single Correct Answer)
+2
-0.5
Change Language
Let z1 and z2 be complex numbers such that z1 $$ \ne $$ z2 and |z1| = |z2|. If Re(z1) > 0 and Im(z2) < 0, then $${{{z_1} + {z_2}} \over {{z_1} - {z_2}}}$$ is
A
one
B
real and positive
C
real and negative
D
purely imaginary
3
WB JEE 2018
MCQ (Single Correct Answer)
+2
-0.5
Change Language
From a collection of 20 consecutive natural numbers, four are selected such that they are not consecutive. The number of such selections is
A
284 $$ \times $$ 17
B
285 $$ \times $$ 17
C
284 $$ \times $$ 16
D
285 $$ \times $$ 16
4
WB JEE 2018
MCQ (Single Correct Answer)
+2
-0.5
Change Language
The least positive integer n such that $${\left( {\matrix{ {\cos \pi /4} & {\sin \pi /4} \cr { - \sin {\pi \over 4}} & {\cos {\pi \over 4}} \cr } } \right)^n}$$ is an identity matrix of order 2 is
A
4
B
8
C
12
D
16
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