Chứng minh: (ac + bd)² + (ad - bc)² = (a² +b² (c²+d²)

No.
Date
a, CM: (ac + bd)² + (ad - bc)² = (a² +b² (c²+d²)
b) CM bott
27
(ac + bd)² < (a² +b²) (c²+d²)