bonjour

trop long quand même , j'en fais 2

f (x) = x² - 4 x + 3

f (x) =  ( x - 1 ) ( x - 3 ) = x² - 3 x - x + 3 = x² - 4 x + 3

f (x) = ( x - 2 )² - 1 =   x² - 4 x + 4 - 1 =  x²  - 4 x + 3

f ( - 1 ) =  ( - 1 )² - 4 *-1 + 3 = 1 + 4 + 3 =  8

f (x) = 0

( x - 1 ) ( x - 3 ) = 0

x = 1 ou 3

x² - 4 x + 3 = 3

x² - 4 x =  0

x ( x - 2 ) = 0

x = 0 ou 2

( x - 2 )² - 1 = 15

( x - 2 )² - 1 - 15 = 0

( x - 2 )² - 16 = 0

( x - 2 - 4 ) ( x - 2 + 4 ) = 0

( x - 6 ) ( x + 2 ) = 0

x = 6 ou - 2

( 1 + x ) /  ( 5 + x ) =  3/5

5 + 5 x = 15 + 3 x

5 x - 3 x = 15 - 5

2 x = 10

x = 10/2 = 5

6/10 = 3/5