Đáp án:
`=2axby+2bycz+2azcx-b^2x^2-c^2x^2-a^2y^2-c^2y^2-a^2z^2-b^2z^2`
Giải thích các bước giải:
`(ax+by+cz)^2-(x^2+y^2+z^2).(a^2+b^2+c^2)`
`=a^2x^2+b^2y^2+c^2z^2+2axby+2bycz+2azcx-a^2x^2-b^2x^2-c^2x^2-a^2y^2-b^2y^2-c^2y^2-a^2z^2-b^2z^2-c^2z^2`
`=2axby+2bycz+2azcx-b^2x^2-c^2x^2-a^2y^2-c^2y^2-a^2z^2-b^2z^2`