помогите пожалуйста решить №369,373,374. Ответ к 369: а) (4; -2) б) (4;8) в) (1...

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помогите пожалуйста решить №369,373,374.
Ответ к
369: а) (4; -2) б) (4;8) в) (1;0)
373: a) (14;-2) б) (5;-2)
374: Обед - 30 ЛТ, ночёвка - 60 ЛТ

Answers & Comments

nafanya2014

Verified answer

369a)
$\left \{ {{x+y=2} \atop {x-y=6}} \right.\Rightarrow \left \{ {{y=2-x} \atop {x-(2-x)=6}} \right.\Rightarrow \left \{ {{y=2-x} \atop {2x=8}} \right.\Rightarrow x=4, y=2-4=-2$
369б)
$\left \{ {{x+y=12} \atop {3x-y=4}} \right.\Rightarrow \left \{ {{y=12-x} \atop {3x-(12-x)=4}} \right.\Rightarrow \left \{ {{y=12-x} \atop {3x-12+x=4}} \right.\Rightarrow \left \{ {{y=12-x} \atop {4x=16}} \right.$
x=4, y=12-4=8
369в)
$\left \{ {{2x-y=2} \atop {3x-2y=3}} \right.\Rightarrow \left \{ {{y=2x-2} \atop {3x-2(2x-2)=3}} \right.\Rightarrow \left \{ {{y=12-x} \atop {3x-4x+4=3}} \right.\Rightarrow \left \{ {{y=12-x} \atop {-x=-1}} \right. 
$
х=1 у=2·1-2=0

373
$\left \{ {{x+4y=6} \atop {x-2y=18}} \right.\Rightarrow \left \{ {{x=6-4y} \atop {6-4y-2y=18}} \right.\Rightarrow \left \{ {{x=6-4y} \atop {-6y=12}} \right.\Rightarrow \left \{ {{x=6-4\cdot(-2)=12-x} \atop {y=-2}} \right.$
x=14 y=-2
$\left \{ {{3x-y=17} \atop {y=8-2x}} \right.\Rightarrow \left \{ {{3x-(8-2x)=17} \atop {y=8-2x}} \right.\Rightarrow \left \{ {{3x-8+2x=17} \atop {y=8-2x}} \right.\Rightarrow \left \{ {{3x+2x=17+8} \atop {y=8-2x}} \right.$
x=5 y=8-2·5=-2

Задача
$\left \{ {{3o+2n=210} \atop {4o+3n=300}} \right. \Rightarrow\left \{ {{9o+6n=630} \atop {-8o-6n=-600}} \right. \Rightarrow$

Складываем уравнения обед=630-600
обед=30 литов
2 ночлега=210-3 обеда=210-3·30=120
1 ночлег = 60 литов

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