1
NDA 2018 Paper 1
MCQ (Single Correct Answer)
+2.5
-0.83
If $$A = \left( {\matrix{ 1 & 2 \cr 2 & 3 \cr } } \right)$$ and $${A^2} - kA - {I_2} = O$$, where I2 is the 2 $$\times$$ 2 identity matrix, then what is the value of k?
A
4
B
$$-$$ 4
C
8
D
$$-$$ 8
2
NDA 2018 Paper 1
MCQ (Single Correct Answer)
+2.5
-0.83
What is the inverse of the matrix $$A = \left( {\matrix{ {\cos \theta } & {\sin \theta } & 0 \cr { - \sin \theta } & {\cos \theta } & 0 \cr 0 & 0 & 1 \cr } } \right)$$ ?
A
$$\left( {\matrix{ {\cos \theta } & { - \sin \theta } & 0 \cr {\sin \theta } & {\cos \theta } & 0 \cr 0 & 0 & 1 \cr } } \right)$$
B
$$\left( {\matrix{ {\cos \theta } & 0 & {\sin \theta } \cr 0 & 1 & 0 \cr {\sin \theta } & 0 & {\cos \theta } \cr } } \right)$$
C
$$\left( {\matrix{ 1 & 0 & 0 \cr 0 & {\cos \theta } & { - \sin \theta } \cr 0 & {\sin \theta } & {\cos \theta } \cr } } \right)$$
D
$$\left( {\matrix{ {\cos \theta } & {\sin \theta } & 0 \cr { - \sin \theta } & {\cos \theta } & 0 \cr 0 & 0 & 1 \cr } } \right)$$
3
NDA 2019 Paper 2
MCQ (Single Correct Answer)
+2.5
-0.83
If $$A = \left[ {\matrix{ 1 & { - 1} \cr { - 1} & 1 \cr } } \right]$$, then the expression A3 $$-$$ 2A2 is
A
a null matrix
B
an identity matrix
C
equal to A
D
equal to $$-$$ A
4
NDA 2019 Paper 2
MCQ (Single Correct Answer)
+2.5
-0.83
If $$A = \left( {\matrix{ 1 & 2 \cr 2 & 3 \cr 3 & 4 \cr } } \right)$$ and $$B = \left( {\matrix{ 1 & 2 \cr 2 & 1 \cr } } \right)$$, then which one of the following is correct?
A
Both AB and BA exist
B
Neither AB nor BA exists
C
AB exists but BA does not exist
D
AB does not exist but BA exists
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