cond :( 4 - x ) /( 2x -1 ) ≥ 0
x - ∞ 1/2 4 +∞
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4-x + + + + + + 0 - - - - -
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2x-1 - - - 0 + + + + + + + + +
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(4-x) /(2x-1) - - I + + + +0 - - - - - - -
radical pozitiv daca x ∈ ( 1/2 ,4]