Question

aplicando o método mais conveniente para o caso , resolva os seguintes sistemas.

a)
x-y=1
-x+2y=3

b)
x=3y
x-2y=3

Answer 1

$\mathrm{\left \{ {{x-y=1\ \mathbf{(I)}} \atop {-x+2y=3\ \mathbf{(II)}}} \right.}\\\\ \mathrm{Somando\ 2.I\ com\ II:}\\\\ \mathrm{2x-2y-x+2y=2+3\ \to\ x=5}\\\\ \mathrm{Substituindo\ x\ em\ I:}\\\\ \mathrm{5-y=1\ \to\ y=5-1\ \to\ y=4}\\\\\\ \mathrm{\left \{ {{x=3y\ \mathbf{(I)}} \atop {x-2y=3\ \mathbf{(II)}}} \right.}\\\\ \mathrm{Substituindo\ x\ em\ II:}\\\\ \mathrm{3y-2y=3\ \to\ y=3}\\\\ \mathrm{Substituindo\ y\ em\ I:}\\\\ \mathrm{x=3.3\ \to\ x=9}$