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Mathematics

If 12\dfrac{1}{2} is a root of the quadratic equation 4x2 - 4kx + k + 5 = 0 , then the value of k is

  1. -6
  2. -3
  3. 3
  4. 6

Quadratic Equations

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Answer

Given ,

12\dfrac{1}{2} is a root of the quadratic equation 4x2 - 4kx + k + 5 = 0

4(12)24k(12)+k+5=012k+k+5=0k+6=0k=6\therefore 4\Big(\dfrac{1}{2}\Big)^2 - 4k\Big(\dfrac{1}{2}\Big) + k + 5 = 0 \\[0.5em] \Rightarrow 1 - 2k + k + 5 = 0 \\[0.5em] \Rightarrow -k + 6 = 0 \\[0.5em] k = 6

∴ Option 4 is the correct option

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