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Question

Question: If f(x) = \(\left| \begin{matrix} a & - 1 & 0 \\ ax & a & - 1 \\ ax^{2} & ax & a \end{matrix} \right...

If f(x) = a10axa1ax2axa\left| \begin{matrix} a & - 1 & 0 \\ ax & a & - 1 \\ ax^{2} & ax & a \end{matrix} \right|, then f(2x) –f(x) equals

A

a (2a + 3x)

B

ax (2a + 3x)

C

ax (2x + 3a)

D

x (2a + 3x)

Answer

ax (2a + 3x)

Explanation

Solution

Apply R2 → R2 – xR1, R3 → R3 –xR2 we get

f(x) = a100a+x100a+x\left| \begin{matrix} a & - 1 & 0 \\ 0 & a + x & - 1 \\ 0 & 0 & a + x \end{matrix} \right|= a (a + x)2

f(2x) – f(x) = a(a + 2x)2 – a (a + x)2 = ax (2a + 3x)