Bonsoir
Politesse !
Développer :
A = (x+5)(x-5)
A = x×x-5x+5x-5×5
A = x²-5x+5x-5×5
A = x²-5x+5x-25
A = x²-25
B = (3x+8)(3x-8)
B = 3x×3x-3x×8+8×3x-8×8
B = 9x²-3x×8+8×3x-8×8
B = 9x²-24x+8×3x-8×8
B = 9x²-24x+24x-8×8
B = 9x²-24x+24x-64
B = 9x²-64
C = (2t+3)(2t-3)
C = 2t×2t-2t×3+3×2t-3×3
C = 4t²-2t×3+3×2t-3×3
C = 4t²-6t+3×2t-3×3
C = 4t²-6t+6t-3×3
C = 4t²-6t+6t-9
C = 4t²-9
Bonne soirée.