Question

Oii,podem me ajudar com essa questão?

Resolva as equações de duas incógnitas a seguir:

1)X+y= 13
X+5y=20

2)X-y=5
X-y=7

3)2x-y=0
X+y=15

Answer 1

Resposta:

$~~~~~~~x+y=13~~.(-1)=\\ \\~~~~~~~~-x-~y=-13\\+~~~~~~~x+5y=~~~20\\~~~~~~~--------\\~~~~~~~~~~~~0+4y=~~~7\\ \\4y=7\\ \\y=\frac{7}{4}\\ \\x+y=13\\ \\x+\frac{7}{4}=13\\ \\\frac{4x+7=52}{4}\\ \\4x+7=52\\ \\4x=52-7\\ \\4x=45\\ \\S~~\left \{ {{x=45/4;~~y=\frac{7}{4} } \}} \right.$

$2)\\ \\~~~~~~~~x-y=5\\+~~~~x+y=7\\~~~~~------\\~~~~~~2x+0=12\\ \\2x=12\\ \\x=\frac{12}{2}\\ \\x=6\\ \\x+y=7\\ \\6+y=7\\ \\y=7-6\\ \\y=1\\ \\S~~\left \{ {{x=6;~~y=1} \}} \right.$

$3)\\ \\~~~~~~~~2x-y=~~0\\+~~~~~~x+y=15\\~~~~~~-------\\~~~~~~~~3x+0=~15\\ \\3x=15\\ \\x=\frac{15}{3}\\ \\x=5\\ \\x+y=15\\ \\5+y=15\\ \\y=15-5\\ \\y=10\\ \\S~~\left \{ {{x=5;~~y=10} \}} \right.$