Chứng minh rằng
Chứng minh rằng :
a) (a²-b²)(c²-d²) = (ac + bd)² - (ad + bc)²;
b)2(a² + b³ + c³ - 3abc) = (a + b + c)[(a - b)² + (b − c)² + (c-a)²];
c) (a + b) (b + c)(c + a) + 4abc = c(a + b)² + a(b + c)²+ b(c + a)²;
d) (a+b+c)³ = a³ + b³ + c3 + 3(a + b)(b + c)(c + a)
a) (a²-b²)(c²-d²) = (ac + bd)² - (ad + bc)²;
b)2(a² + b³ + c³ - 3abc) = (a + b + c)[(a - b)² + (b − c)² + (c-a)²];
c) (a + b) (b + c)(c + a) + 4abc = c(a + b)² + a(b + c)²+ b(c + a)²;
d) (a+b+c)³ = a³ + b³ + c3 + 3(a + b)(b + c)(c + a)