Question

3x+4y= -5

x-2y= 5


Como faz no metodo de adição

Answer 1

$3x+4y=-5~....~equacao~I\\ ~~x-2y~=~5~...~equacao~II\\ \\ Multiplique~a~equacao~II~por~(2)~para~isolar~a~incognita~"x";\\ some~as~duas~equacoes~e~obtenha~o~valor~de~"x";\\ substitua~o~valor~de~"x"~em~uma~das~equacoes.\\ \\ x-2y=5~~.(2)=2x-4y=10\\ \\ ~~~~~~~~3x+4y=-5\\~+~~~~2x-4y=10\\~~~~~~~-------\\~~~~~~~~5x+~~0=~5\\ \\ 5x=5\\ \\ x=\frac{5}{5}\\ \\ x=1\\ \\ substitua~(x=1)~em~uma~das~equacoes:\\ \\ 3x+4y=-5\\ \\ 3.(1)+4y=-5\\ \\ 3+4y=-5\\ \\ 4y=-5-3$

$4y=-8\\ \\ y=-\frac{8}{4} \\ \\ y=-2~~~~~~~~~~~~S=(x=1;~~y=-2)$