Решите двойное неравенство

Объяснение:

2A . 15 .    . . . = [( a² + b² - ( a - b )²]/( a² - b²) =( a² + b²- a²+ 2ab- b²)/(a² - b²) =

= 2ab/( a² - b²) .

16 .   . . . = [( a - b )²- ( a + b )²]/( a² - b²)] = ( a²- 2ab + b²- a²- 2ab -b²)/(a² - b²) =

  = - 4ab/( a² - b²) ;

17 .  . . . = ( 4x - 4x + 4y )/( x² - y² ) = 4y/( x² - y² ) ;

18 .  . . . = [ 3y² * 3( x - y ) ]/[ ( x² - y² )y ] = 9y/( x + y ) ;

19 .  . . . = [ ( x² - y² ) * 2y ]/[ 2xy( x - y ) ] = ( x + y )/x ;

20 .  . . . = ( x² - y²)/ y² : ( 7x - 7y )/y = ( x² - y²)/ y² * y/7( x - y ) = ( x + y )/7y .  

{2(x-2y)=x-8y
{5(x+y)=2(x-y)+10
{2x-4y=x-8y
{5x+5y=2x-2y+10
{2x-4y-x+8y=0
{5x+5y-2x+2y=10
{x+4y=0|*3
{3x+7y=10
-{3x+12y=0
-{3x+7y=10
5y=10|:5
y=2
3x+12*2=0
3x=-24|:3
x=-8
{3(x+4y)-4x=2(2x+y)
{7(x-5y)+6x=3(x+4y)+27
{3x+12y-4x=4x+2y
{7x-35y+6x=3x+12y+27
{-x+12y-4x-2y=0
{13x-35y-3x-12y=27
{-5x+10y=0|*2
{10x-47y=27
+{-10x+20y=0
+{10x-47y=27
-27y=27|:(-27)
y=-1
-10x-1*20=0
-10x=20|:(-10)
x=-2
{15+2(x+3y)=3(4x+y)
{2(5x-y)-3y=2+3(2x-y)
{15+2x+6y=12x+3y
{10x-2y-3y=2+6x-3y
{2x+6y-12x-3y=-15
{10x-5y-6x+3y=2
{-10x+3y=-15|*2
{4x-2y=2|*3
+{-20x+6y=-30
+{12x-6y=6
-8x=-24|:(-8)
x=3
12*3-6y=6
-6y=6-36
-6y=-30|:(-6)
y=5
{5(7x+2y)-11y=6(2x+y)+2 {33+3(6x-5y)=3(x+2y)-5y
{35x+10y-11y=12x+6y+2
{33+18x-15y=3x+6y-5y
{35x-y-12x-6y=2
{18x-15y-3x-6y+5y=-33
{23x-7y=2|*16
{15x-16y=-33|*7
-{368x-112y=32
-{105x-112y=-231
263x=263|:263
x=1
15*1-16y=-33
-16y=-33-15
-16y=-48|:(-16)
y=3