Factoriser : A(x): 4x²-25-(2x+5)(3x-1) Calculer:A(5/2) A(- √ 2)

A(x) =2x2-13x-20=  (x+4) (2x+5)


Calculer : 
A(5/2)
=2.5
-√2
=....

Bonjour,

1) A(x) = 4x² - 25 - (2x + 5)(3x - 1)
A(x) = (2x + 5)(2x - 5) - (2x + 5)(3x - 1)
A(x) = (2x + 5)[(2x - 5) - (3x - 1)]
A(x) = (2x + 5)(2x - 5 - 3x + 1)
A(x) = (2x + 5)(-x - 4)

2) [tex]A(\dfrac{5}{2}) = (2\times\dfrac{5}{2} + 5)(-\dfrac{5}{2} - 4)\\\\A(\dfrac{5}{2}) = (5+ 5)(-\dfrac{5}{2} -\dfrac{8}{2})\\\\A(\dfrac{5}{2}) = 10\times(-\dfrac{13}{2})\\\\A(\dfrac{5}{2}) = 5\times(-13)\\\\A(\dfrac{5}{2}) = -65[/tex]

[tex]A(-\sqrt{2}) = [2\times(-\sqrt{2}) + 5][-(-\sqrt{2}) - 4]\\\\A(-\sqrt{2}) = (-2\sqrt{2} + 5)(\sqrt{2} - 4)\\\\A(-\sqrt{2}) = -2\sqrt{2}\times\sqrt{2}+8\sqrt{2}+5\sqrt{2}-20\\\\A(-\sqrt{2}) = -4+13\sqrt{2}-20\\\\A(-\sqrt{2}) = 13\sqrt{2}-24[/tex]