math 問題

(x/4 + 2y)²
= (x/4)² + 2(x/4)(2y) + (2y)²
= x²/16 + xy + 4y²

(2 - 4x/5) (2 + 4x/5)
= 2² - (4x/5)²
= 4 - 16x²/25

- (3x - y/4)²
= - [(3x)² - 2(3x)(y/4) + (y/4)²]
= - [9x² - 3y/2 + y²/16]
= - 9x² + 3y/2 - y²/16

2012-07-19 00:27:53 補充：
修正 :

- (3x - y/4)²
= - [(3x)² - 2(3x)(y/4) + (y/4)²]
= - [9x² - 3xy/2 + y²/16]
= - 9x² + 3xy/2 - y²/16