4x⁴ + x⁴ - 2x² + 1 - 1 - 3 =
= 4x⁴ + ( x⁴ - 2x² + 1 ) - 4
= ( 4x⁴ - 4) + ( x² - 1)²
= 4· ( x² - 1)·(x² + 1) + ( x² - 1)²
= ( x² - 1) [ 4·( x² + 1) + ( x² - 1) ]
= ( x² -1) · ( 4x² + 4 + x² -1)
= ( x² - 1 ) · ( 5x² + 3) = 0
daca x² -1= 0 ; ( x -1 ) · ( x + 1) = 0
x₁ = 1 ; x₂ = - 1
5x² + 3 =0 , adica 5x² = - 3 ; x² = - 3 / 5 nu are solutii reale
x² < 0 este fals in R
