ав+ас+4в+4с = а(в+с)+4(в+с) = (а+4) (в+с)
F'(x) = (-3x^8 +2 tg x +√-x +5 ln x -7)' =<span> -24х^7+2/cos</span>²<span> x - 1/2 </span>√<span>-х + 5/х</span>
(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.
{x²+y²=20
{2y-x=0
{x=2y
{(2y)²+y²=20
{4y²+y²=20
{x=2y
{5y²=20
{x=2y
{y²=4
{x=2y
{|y|=2
{x=2y
y=2⇒x=2*2=4
y=-2⇒x=-4
Ответ: (4;2) , (-4;-2)