25 - 12x + (x - 5)(x + 5) - (5 - x)²
= 25 - 12x + x² + 5x - 5x - 25 - (25 - 10x + x²= 25 - 12x + x² + 5x - 5x - 25 - 25 + 10x - x= 25 - 12x + x² + 5x - 5x - 25 - 25 + 10x - x= 0
25 - 12x + (x - 5)(x + 5) - (5 - x)²
= 25 - 12x + x² + 5x - 5x - 25 - (25 - 10x + x²
= 25 - 12x + x² + 5x - 5x - 25 - 25 + 10x - x
= 25 - 12x + x² + 5x - 5x - 25 - 25 + 10x - x
= 0