(√15 + √12 +√5 +2) *x² =(√15 - √12 +√5 - 2)
(√15 + 2√3 +√5 +2) *x² = (√15 -2√3 +√5 -2)
[√3 (√5+2) + 1(√5+2)] *x² = [√3(√5-2) +1 (√5-2)]
(√5+2)* (√3+1) * x² = (√5-2) * ( √3+1)
(√5+2) * x² = (√5-2)
x² = (√5-2) : (√5+2)
x² = (√5-2) * (√5-2) : (√5²-2²)
x² =(√5-2)² :(5-4)
x² = (√5-2)² ⇒ x= √5-2 sau x= 2-√5 ⇒ x∈{√5-2 ; 2-√5}