bjr
x² = -2
un carré est toujours positif => impossible.. pas de solution
x² = 7
x² - 7 = 0
(x + √7) (x - √7= 0
=> x = -√7 ou √7
x² - 7 ≤ 0
x -∞ -√7 +√7 +∞
x+√7 - + +
x-√7 - - +
x²-7 + - +
=> x² - 7 ≤0 qd x € [-√7 ; √7]
f(x) = x³
f(-4) = (-4)³ = -4 x (-4) x (-4) = -64
x³ = -64
=> x = -4
