bonjour
f (x) = 4 / ( 1 + x²)
f ( 3/4 ) = 4 / ( 1 + 3/4² ) = 4 / ( 1 + 9/16 ) = 4 / ( 25/16 )
= 4 * 16/25 = 64/25 = 2.56
f ( 2/3 ) = 4 / ( 1 + 4/9) = 4 / ( 13/9 ) = 4 x 9/13 = 36/13
4 /( 1 + x )² = 3
4 = 3 + 3 x²
- 3 x² = 3 - 4
- 3 x² = - 1
x² = 1/3
x = √1/3 ou - √ 1/3
