Bonsoir

a. Volume parallélépipède = L × l × h

V1 (x) = AB × AC × BF = 9 × x

V1 (x) = 9x

Volume pyramide = 1/3 aire de la base × hauteur

V2 (x) = 1/3 × EF² × SM = 1/3 × 9 × (7-x)

V2 (x) = 3 (7-x)

V2 (x) = 21 - 3x

c. On veut V1 (x) = V2 (x)

9x = 21 - 3x

12x = 21

x = 21/12 = 1,75

d. On veut V1 (x) = 2 V2 (x)

9x = 2 ( 21 - 3x )

9x = 42 - 6x

15x = 42

x = 42/15 = 2,8