Question

resolva os sistemas.
a)x=y-5
y=2x+8

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

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

ME AJUDEM E PR HOJE!!!!!!

Answer 1

$a)x=y-5\\y=2x+8\\\\\\\\y=2x+8\to y=2(y-5)+8\to\\\\ y=2y-10+8\to \\\\ y-2y=-10+8\to\\\\ -y=-2\to \\\\y=2\\\\\\x=y-5\to\\\\ x=2-5\to\\\\ x=-3\\\\\\\\ S=(-3;2)$





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





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