Chứng minh hằng đẳng thức: (a+b+c)^3 -a^3 -b^3 -c^3 = 3(a+b)
Giải thích
a+b+c3−a3−b3−c3=a+b+c3−a3−b3+c3=b+ca+b+c2+aa+b+c+a2−b+cb2−bc+c2=b+c3a2+3ab+3ac+3bc=3a+bb+cc+a
a+b+c3−a3−b3−c3=a+b+c3−a3−b3+c3=b+ca+b+c2+aa+b+c+a2−b+cb2−bc+c2=b+c3a2+3ab+3ac+3bc=3a+bb+cc+a