a. 3(x - y)² - 2(x + y)² - (x - y)(x + y)

= 3(x² - 2xy + y²) - 2(x² + 2xy + y²) - (x² - y²)

= 3x² - 6xy + 3y² - 2x² - 4xy - 2y² - x² + y²

= - 10xy + 2y²

b. 2(2x + 5)² - 3(4x + 1)(1 - 4x)

= 2(4x² + 20x + 25) - 3(1 + 4x)(1 - 4x)

= 8x² + 40x + 50 - 3(1 - 16x²)

= 8x² + 40x + 50 - 3 + 48x²

= 56x² + 40x + 47

pn coi kt lại nhé

4) 4a² - 4a + 1=(2a - 1)²

5) -9x² + 6xy - y²

= - (9x² - 6xy + y²)= - (3x - y)²

6) -6x + 9 + x²

= x² - 6x + 9 = (x - 3)²

7) 4x² - 4x + 1 - y²

= (2x - 1)² - y² = (2x - 1 - y)(2x - 1 + y)

pn kt lại nha

1) x² - 2xy + y² - x²

=(x - y)² - x²

=(x - y - x)(x - y + x)= -y(2x - y)

2) x² - 2xy - 4z² + y²

= x² - 2xy + y² - 4z²

= (x - y)² - (2z)² = (x - y - 2z)(x - y + 2z)

3) (2x + 1)² - (x - 1)²

=(2x + 1 - x + 1)(2x + 1 + x - 1)=3x(x + 2)

Pn coi kt lại số nha

7:0=0

0.8=0

0.369=0

như vậy :1473862569+0=1473862569

Vậy x= - 0,7 nha, mk đánh lộn xin lỗi, hihi

12 - 1/2 + 2x= 8 - 3x

12 - 1/2 - 8= -3x - 2x

-5x= 3,5

=> x= - 0,7

Vậy x= 0,7

Gọi CTTQ: NxOy

Ta có: 30,43= x * 14/46 * 100

=> x= 30,43 * 46/1400= 1

%O= 100% - 30,43%= 69,57%

69,57= y * 16/46 * 100

=> y= 69,57 * 46/1600=2

=> CT : NO2