Question

1)Resolva os sistemas:
a){3x+2y+40
x-3y=-5

b){x-y=5
x=2y+1

c){x+y=9
x-y=5

Answer 1

$a)3x+2y+40\\x-3y=-5\\\\\\ x-3y=-5\to x=3y-5\\\\\\ 3x+2y+40 \to 3*(3y-5)+2y+40 \to 9y-15+2y+40 \to \\ 11y=-40+15\to 11y=-25\to y= \frac{-25}{11} \\\\\\x=3y-5\to x=3(\frac{-25}{11})-5\to x=\frac{-75}{11}-5\to x=\frac{-80}{11}\\\\\\ S=\frac{-80}{11};\frac{-25}{11})$





$b)x-y=5\\x=2y+1\\\\\\x-y=5\to x=y+5\\\\\\ x=2y+1\to y+5=2y+1\to y-2y=1-5\to -y=-4\to y=4\\\\\\ x=y+5\to x=4+5\to x=9\\\\\\\\ S=(9,4)$





$c)x+y=9\\x-y=5\\\\\\x+y=9\to x=-y+9\\\\\\ x-y=5\to -y+9-y=5\to -2y=5-9\to -2y=-4\to y= \frac{-4}{-2} \to\\ y=2\\\\\\ x=-y+9\to x=-2+9\to x=7\\\\\\\\ S=(7;2)$