(b+c-2a)(c-b)+(c+a-2b)(a-c)-(a+b-2c)(a-b)=
=bc+c²-2ac-b²-bc+2ab+ac+a²-2ab-c²-ac+2bc-a²-ab+2ac+ab+b²-2bc=
=(bc-bc+2bc-2bc)+(ac-ac+2ac-2ac)+(ab-ab+2ab-2ab)+(a²-a²+b²-b²+c²-c²)≡0.
Применены свойства степени
<h3>
Решить уравнение.</h3>
![\tt3x - 42 = 6x + 18;\\3x - 6x = 18 + 42;\\-3x = 60;\\x = \dfrac{60}{-3};\\x = -20.](https://tex.z-dn.net/?f=%5Ctt3x%20-%2042%20%3D%206x%20%2B%2018%3B%5C%5C3x%20-%206x%20%3D%2018%20%2B%2042%3B%5C%5C-3x%20%3D%2060%3B%5C%5Cx%20%3D%20%5Cdfrac%7B60%7D%7B-3%7D%3B%5C%5Cx%20%3D%20-20.)
<h3><u>Ответ</u>: -20.</h3>