Question

Utilizar el método de suma y resta:

1) x+y=10
-x+y=2

2)5x+y=10
x-y=18

3)5x+3y=10
x-3y=8

4)3x+y=5
x-y=7

Answer 1

1) -x+y=2 -->y=2+x       x+y=10 -->Sustituir--> x+2+x=10 --> 2x+2=10 --> 2x=8

x=8/2 --> x=4 --> Sustituir --> 4+y=10 --> y=6

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2) x-y=18 --> x=18+y    5x+y=10 --> 5(18+y) +y=10 --> 90+5y+y=10 --> 90+6y=10

90-10=-6y --> y=80/-6 -->  y=-13,333 --> Sustituir--> x-(-13,333)=10 --> x=4,667

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3) x-3y=8 --> x=8+3y --> Sustituir --> 5(8+3y)+3y=10 --> 40+15y+3y=10

40+18y=10--> 40-10=-18y --> y=30/-18 --> y=-1,667 --> Sustituir--> x-3(-1,667)=8

x=8-5 --> x=3

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4) x-y=7 --> x=7+y --> Sustituir --> 3(7+y) +y=5 --> 21+3y+y=5 --> 21+4y-5=0

21-5=-4y -->y=16/-4 --> y=-4 --> Sustituir --> x-(-4)=7 --> x+4=7 --> x=3