Y=-sin(3/2+пи/2)
y=(sin(3/2)cos(пи/2)+cos(3/2)sin(пи/2))
y=-(sin(3/2)*0+cos(3/2)*1)
y=-(0+cos(3/2))
y=-cos(3/2)
![\left \{ {{3x+y=7} \atop {9x-2y=1}} \right. \\\\ \left+ \{ {{6x+2y=14} \atop {9x-2y=1}} \right.](https://tex.z-dn.net/?f=+%5Cleft+%5C%7B+%7B%7B3x%2By%3D7%7D+%5Catop+%7B9x-2y%3D1%7D%7D+%5Cright.+%5C%5C%5C%5C+%5Cleft%2B+%5C%7B+%7B%7B6x%2B2y%3D14%7D+%5Catop+%7B9x-2y%3D1%7D%7D+%5Cright.+)
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15x = 15
x = 1
y = 7 - 3x = 7 - 3 * 1 = 7 - 3 = 4
Ответ : (1 ; 4)
![\left \{ {{4x-y=10} \atop {x=2y-1}} \right.\\\\ +\left \{ {{-8x+2y=-20} \atop {x-2y=-1}} \right.](https://tex.z-dn.net/?f=+%5Cleft+%5C%7B+%7B%7B4x-y%3D10%7D+%5Catop+%7Bx%3D2y-1%7D%7D+%5Cright.%5C%5C%5C%5C++%2B%5Cleft+%5C%7B+%7B%7B-8x%2B2y%3D-20%7D+%5Catop+%7Bx-2y%3D-1%7D%7D+%5Cright.+)
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- 7x = - 21
x = 3
y = 4x - 10 = 4 * 3 - 10 = 12 - 10 = 2
Ответ : (3 ; 2)
72/( Х + 5 ) + 54/( Х - 5 ) = 9( х^2 - 25 )
72( Х - 5 ) + 54( Х + 5 ) = 9( х^2 - 25 )
72х - 360 + 54х + 270 = 9( х^2 - 25 )
126х - 90 = 9х^2 - 225
9х^2 - 126х - 135 = 0
9( x^2 - 14x - 15 ) = 0
D = 196 + 60 = 256 = 16
X1 = ( 14 + 16 ) : 2 = 15 ( км/час ) собственная скорость баржи
Х2 = ( 14 - 16 ) : 2 = - 1 ( < 0 )
Ответ 15 км/час
Решение показано на фото в приложении.