Bonsoir
A = 9x² +12x +49
A = (3x +7)²
et B = 25 -20x +4x²
B = (5 -2x)²
C = A -B
C = (3x +7)² - ( 5 -2x)²
C = (3x+7 +5 -2x)(3x+7 -5 +2x)
C = (x+12)(5x +2)
Pour x = 0
C = 12 x 2 = 24
Pour x = - 2/5
C = (-2/5 +12)( -10/5 +2)
C = ( -2/5 + 60/5) ( -10/5 + 10/5)
C = 58/5 x 0 = 0