Cho x + y + z = 0. chứng minh rằng x^3 + y^3 + z^3 = 3xyz
Giải thích
Ta có: x3+y3+z3
=x+y3−3xyx+y+z3=x+y3+z3−3xy.−z(do x+y+z=0⇒x+y=−z)=x+y+zx+y2−x+yz+z2+3xyz=3xyzdo x+y+z=0
Ta có: x3+y3+z3
=x+y3−3xyx+y+z3=x+y3+z3−3xy.−z(do x+y+z=0⇒x+y=−z)=x+y+zx+y2−x+yz+z2+3xyz=3xyzdo x+y+z=0