bonsoir
f (x) = 4 x² - 9 x + 2
α = 9 / 8
β = 4 ( 9/8 )² - 9 * 9/8 + 2 = 4 * 81/64 - 81/8 + 2 = 324/64 - 648/64 + 128/64
β = - 196
f (x) = 4 ( x - 9/8 ) ² - 196
f (x) = 4 ( x - 9/8 - 14 ) ( x - 9/8 + 14 ) = 4 ( x - 9/8 - 112/8 ) ( x - 9/8 + 112/8)
f (x ) = 4 ( x - 121/8 ) ( x + 103 /8 )
f (x) = 0
4 x² - 9 x + 2 = 0
Δ = 81 - 4 ( 4 x 2 ) = 81 - 32 = 49 = 7 ²
x 1 = ( 9 - 7 ) / 8 = 2/8 = 1/4
x 2 = ( 9 + 7 ) / 8 = 16 /8 = 2
