Question

5)rezolvati prin metoda substitutiei sistemele:
a) x=y+5=2
x+y=11

b)x-y=2
y=2x-2

c)x=2y-1
2x+3y=12


d)5x-4y=-1
y=3x+2

Answer 1

a)x=y+5=2 =>x=y=2-5=>x=y=-3
-3+y=11=>y=11+3=14
-3+14=11
b) x-y=2
x-2x-2=2
-x=2+2
-x=4
x=-4
y=2*(-4)-2
y=-8-2
y=-10
c) x=2y-1
2x+3y=12
2(2y-1)+3y=12
4y-2+3y=12
7y=12+2
y=14:7
y=2
x=2*2-1=4-1=3
x=3
d) 5x-4y=-1
y=3x+2
5x-4(3x+2)=-1
5x-12x-8=-1
-7x=-1+8
-7x=7
x=-1
y=3*(-1)+2
y=-3+2
y=1