(2a+b+c)²-(a-2b+c)²-3a²-3b²+8ab+2ac+6bc=
=((2a+b+c)+(a-2b+c))(2a+b+c)-(a-2b+c))-3a²-3b²+8ab+2ac+6bc=
=(2a+b+c+a-2b+c)(2a+b+c-a+2b-c)-3a²-3b²+8ab+2ac+6bc=
=(3a-b+2c)(a+3b)-3a²-3b²+8ab+2ac+6bc=
=3a²+9ab-ab-3b²+2ac+6bc-3a²-3b²+8ab+2ac+6bc=
=16ab-6b²+4ac+12bc
![( \frac{x+y}{2} )^2-( \frac{x-y}{2} )^2-xy=](https://tex.z-dn.net/?f=%28+%5Cfrac%7Bx%2By%7D%7B2%7D+%29%5E2-%28+%5Cfrac%7Bx-y%7D%7B2%7D+%29%5E2-xy%3D)
![=(\frac{x+y}{2} +\frac{x-y}{2} )( \frac{x+y}{2} -\frac{x-y}{2} )-xy=](https://tex.z-dn.net/?f=%3D%28%5Cfrac%7Bx%2By%7D%7B2%7D+%2B%5Cfrac%7Bx-y%7D%7B2%7D+%29%28+%5Cfrac%7Bx%2By%7D%7B2%7D+-%5Cfrac%7Bx-y%7D%7B2%7D+%29-xy%3D)
![=(\frac{x+y+x-y}{2}*\frac{x+y-x+y}{2} )-xy=\frac{2x}{2}* \frac{2y}{2} -xy=xy-xy=0](https://tex.z-dn.net/?f=%3D%28%5Cfrac%7Bx%2By%2Bx-y%7D%7B2%7D%2A%5Cfrac%7Bx%2By-x%2By%7D%7B2%7D++%29-xy%3D%5Cfrac%7B2x%7D%7B2%7D%2A+%5Cfrac%7B2y%7D%7B2%7D++-xy%3Dxy-xy%3D0)
В)(3х-5)^2=0
9х^2-30х+25=0
Д=900-4*9*25=900-900=0
х1=30-0/2*9=30/18=5/3
х2=30+0/2*9=30/18=5/3
ответ. 5/3=1 1/3
{x²+y²-xy=31⇒(x-y)²+xy=31
{x²y-xy²=-30⇒xy(x-y)=-30
делаем замену x-y=a,xy=b
{a²+b=31⇒b=31-a²
{ab=-30⇒(31-a²)a=-30
a³-31a-30=0
a²(a+1)-a(a+1)-30(a+1)=0
(a+1)(a²-a-30)=0
(a+1)(a(a-6)+5(a-6))=0
(a+1)(a+5)(a-6)=0
1)a+1=0⇒a=-1 b=31-1=30
{x-y=-1⇒x=y-1
{xy=30
y²-y-30=0
y1+y2=1 U y1*y2=-30
y1=6 x1=6-1=5
y2=-5 x2=-5-1=-6
2)a+5=0⇒a=-5 b=31-25=6
{x-y=-5⇒x=y-5
{xy=6
y²-5y-6=0
y1+y2=5 U y1*y2=-6
y1=6 x1=6-5=1
y2=-1 x2=-1-5=-6
3)a=6 b=31-36=-5
{x-y=6⇒y+6
{xy=-5
y²+6y+5=0
y1+y2=-6 U y1*y2=5
y1=-1 x1=-1+6=5
y2=-5 x2=-5+6=1
Ответ (5;6);(-6;-5);(1;6);(-6;-1);(5;-1);(1;-5)
Ответ: -3
Объяснение:
любое число, которое меньше или равняется -2