1
WB JEE 2019
MCQ (Single Correct Answer)
+1
-0.25
Change Language
The general value of the real angle $$\theta$$, which satisfies the equation, $$(\cos \theta + i\sin \theta )(\cos 2\theta + i\sin 2\theta )...(\cos n\theta + i\sin n\theta ) = 1$$ is given by, (assuming k is an integer)
A
$${{2k\pi } \over {n + 2}}$$
B
$${{4k\pi } \over {n(n + 1)}}$$
C
$${{4k\pi } \over {n + 1}}$$
D
$${{6k\pi } \over {n(n + 1)}}$$
2
WB JEE 2019
MCQ (Single Correct Answer)
+1
-0.25
Change Language
Let a, b, c be real numbers such that a + b + c < 0 and the quadratic equation ax2 + bx + c = 0 has imaginary roots. Then,
A
a > 0, c > 0
B
a > 0, c < 0
C
a < 0, c > 0
D
a < 0, c < 0
3
WB JEE 2019
MCQ (Single Correct Answer)
+1
-0.25
Change Language
A candidate is required to answer 6 out of 12 questions which are divided into two parts A and B, each containing 6 questions and he/she is not permitted to attempt more than 4 questions from any part. In how many different ways can he/she make up his/her choice of 6 questions?
A
850
B
800
C
750
D
700
4
WB JEE 2019
MCQ (Single Correct Answer)
+1
-0.25
Change Language
There are 7 greeting cards, each of a different colour and 7 envelopes of same 7 colours as that of the cards. The number of ways in which the cards can be put in envelopes, so that exactly 4 of the cards go into envelopes of respective colour is,
A
$${}^7{C_3}$$
B
2 . $${}^7{C_3}$$
C
3! $${}^4{C_4}$$
D
3! $${}^7{C_3}$$$${}^4{C_3}$$
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