Let A=[1234] and B=[abcd] are two matrices such that AB = BA and c≠0, then value of a−d3b−c is :
A
2
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B
-2
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C
-1
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Solution
The correct option is C -1 AB=[1234][abcd]=[a+2cb+2d3a+4c3b+4d]BA=[abcd][1234]=[a+3b2a+4bc+3d2c+4d] If AB = BA, then a + 2c = a + 3b ⇒ 2c = 3b ⇒b≠0 b + 2d = 2a + 4b ⇒ 2a - 2d = -3b a−d3b−c=−32b3b−32b=−1