bonjour
E = x ⁴ - 11 x² + 18 = 0
X² - 11 X + 18 = 0
Δ = ( -11)² - 4 ( 1*18) = 121 - 72 = 49
x 1 = ( 11 - 7) / 2 = 4/2 = 2
x 2 = ( 11 + 7) /2 = 18/2 = 9
x² = 2 ⇔ x = √2 ou ( - √2)
x² = 9 ⇔ x = √ 9 ou ( - √9) = 3 ou - 3
S ( - √2 : √2 ; - 3 ; 3 )
4 x⁴ + 7 x² - 2 = 0
4 X² + 7 X - 2 = 0
Δ = 49 +32 = 81
x 1 = ( - 7 - 9 ) / 8 = - 16 /8 = - 2
x 2 = ( - 7 + 9) /8 = 2/8 = 1 /4
x² = - 2 ⇔ pas de solution dans R
x² = 1/4 ⇔ x = √1/4 ou ( - √1/4)
S ( - √1/4 ; √1/4 )
