1. = x² + 2√3x + 3 - ( 2x² + 4√6x + 12 )
= x² + 2√3x + 3 - 2x² - 4√6x - 12
= - x² + 2√3x - 4√6x - 9
2. = 8x² - ( 2x² + 2√2x + 1
= 8x² - 2x² - 2√2x + 1
= 6x² - 2√2x + 1
3. = 9x²/25 - 6/5xy + y² - 4y²
= 9x² - 6/5xy - 2y²
4. = 4x² + x + 1/16 - ( x² - 3/2x + 9/16 )
= 4x² + x + 1/16 - x² + 3/2x - 9/16
= 3x² + x + 1,5x - 1/2
= 3x² + 2,5x - 0,5
5. = 9 - 6x + x² - 9/4
= x² - 6x + 9 - 2,25
= x2 - 6x + 6,75