Trắc nghiệm Toán 8 Hiệu hai bình phương

 (x² – 4y)(x² + 4y) 

= (x²)² – (4y)² 

= x⁴ – 16y² 

 (x − 6)(x + 6) − (x + 3)² = 9

x² − 36 − x² − 6x − 9 = 9

− 6x = 54

x = − 9

 (x – 5)² – (x + 5)² 

= [(x – 5) – (x + 5)].[(x – 5) + (x + 5)]

= (x – 5 – x – 5).(x – 5 + x + 5)

= – 10 . 2x

= – 20x

 305x.295y 

= 305.295.xy

= [(300 + 5)(300 - 5)].xy

= (300² - 5²).xy

= (90000 - 25).xy

= 89975xy

 3(2² + 1)(2⁴ + 1)(2⁸ + 1)(2¹⁶ + 1)(2³² + 1)

= (2² – 1)(2² + 1)(2⁴ + 1)(2⁸ + 1)(2¹⁶ + 1)(2³² + 1)

= (2⁴ – 1)(2⁴ + 1)(2⁸ + 1)(2¹⁶ + 1)(2³² + 1)

= (2⁸ – 1)(2⁸ + 1)(2¹⁶ + 1)(2³² + 1)

= (2¹⁶ – 1)(2¹⁶ + 1)(2³² + 1)

= (2³² – 1)(2³² + 1)

= (2⁶⁴ – 1)