SOLUTION: Let f(x) = 3x^2 - 4x. Find the constant k such that f(x) = f(k - x) for all real numbers x.

Algebra ->  Functions -> SOLUTION: Let f(x) = 3x^2 - 4x. Find the constant k such that f(x) = f(k - x) for all real numbers x.      Log On


   



Question 1027846: Let f(x) = 3x^2 - 4x. Find the constant k such that f(x) = f(k - x) for all real numbers x.
Answer by ikleyn(52797) About Me  (Show Source):
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Let f(x) = 3x^2 - 4x. Find the constant k such that f(x) = f(k - x) for all real numbers x.
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The condition requires that this identity would hold for all real numbers x:

3x%5E2+-+4x = 3%2A%28k-x%29%5E2+-+4%28k-x%29.

Simplify it step by step

3x%5E2+-+4x = 3k%5E2+-+6kx+%2B+3x%5E2+-+4k+%2B+4x,

3k%5E2+-+6kx+-+4k+%2B+8x = 0.

It would be identically zero if

3k%5E2 = 4k    (1)   and  
6kx = 8x     (2)

are hold simultaneously.

Fortunately,  k = 4%2F3  satisfies both  (1)  and  (2).

Answer.  k = 4%2F3.