(乘法公式)数学题分享

解:ab+bc+ac

=(a+b+c)²－(a²＋b²＋c²)/2

=－1/2

a²b+ab²+b²c+bc²＋a²c＋ac²

=(a＋b＋c)³－(a³＋b³＋c³)

=-2/3－2abc

a²b+ab²+abc＋b²c＋bc²＋abc＋a²c＋ac²＋abc

=ab(a＋b＋c)＋bc(a＋b＋c)＋ac(a＋b＋c)

=(a＋b＋c)(ab＋bc＋ac)=－1/2

=－2/3－2abc+3abc,abc=1/6

a²b²＋b²c²＋a²c²

=(ab＋bc＋ac)²-2abc(a＋b＋c)

=－1/12

a^4+b^4+c^4

=(a²＋b²＋c²)²－2(a²b²＋b²c²＋a²c²)

=25/6