1
WB JEE 2010
MCQ (Single Correct Answer)
+1
-0.25

If $$A = \left[ {\matrix{ 1 & 2 \cr { - 4} & { - 1} \cr } } \right]$$ then A$$-$$1 is

A
$${1 \over 7}\left[ {\matrix{ { - 1} & 2 \cr 4 & 1 \cr } } \right]$$
B
$${1 \over 7}\left[ {\matrix{ 1 & 2 \cr { - 4} & { - 1} \cr } } \right]$$
C
$${1 \over 7}\left[ {\matrix{ { - 1} & { - 2} \cr 4 & 1 \cr } } \right]$$
D
Does not exist
2
WB JEE 2011
MCQ (Single Correct Answer)
+1
-0.25

If A and B are two matrices such that A + B and AB are both defined, then

A
A and B can be any matrices
B
A, B are square matrices not necessarily of the same order
C
A, B are square matrices of the same order
D
number of columns of A = number of rows of B
3
WB JEE 2011
MCQ (Single Correct Answer)
+1
-0.25

If $$A = \left( {\matrix{ 3 & {x - 1} \cr {2x + 3} & {x + 2} \cr } } \right)$$ is a symmetric matrix, then the value of x is

A
4
B
3
C
$$-$$4
D
$$-$$3
4
WB JEE 2011
MCQ (Single Correct Answer)
+1
-0.25

If $$z = \left| {\matrix{ 1 & {1 + 2i} & { - 5i} \cr {1 - 2i} & { - 3} & {5 + 3i} \cr {5i} & {5 - 3i} & 7 \cr } } \right|$$, then $$(i = \sqrt { - 1} )$$

A
z is purely real
B
z is purely imaginary
C
$$z + \overline z = 0$$
D
$$(z - \overline z )i$$ is purely imaginary
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