Bonjour,
A= 3x+24 +28x +8=
31x + 32
B= 5x-5 -14x -21x²=
-21x²-9x -5
C) 21 -14x -8x² +4x=
-8x² -10x +21
x= -2
A= 3* 6 + 4 *-12 =
18 - 48 = -30
x=1/2
B= 5(1/2-1) - 7*1/2 (2 + 3*1/2)
5*(1/2-2/2) - 7/2 ( 2+3/2)
5* -1/2 - 7/2( 4/2+3/2)
-5/2 -7/2 * 7/2
-5/2 -14/4
-5/2 -7/2
-12/2 = -6