y=x-x'=>y'=x'-x''\\ y'=-4x+y=>x'-x''=-4x+x-x'=>x''-2x'-3x=0\\ \lambda^2-2\lambda-3=0=>\lambda=3\;\;\;\;\;\;\;\lambda=-1=>x=C_1e^{3t}+C_2e^{-t}=>x'=3C_1e^{3t}-C_2e^{-t}\\ y=C_1e^{3t}+C_2e^{-t}-3C_1e^{3t}+C_2e^{-t}=-2C_1e^{3t}+2C_2e^{-t}" alt="x'=x-y=>y=x-x'=>y'=x'-x''\\ y'=-4x+y=>x'-x''=-4x+x-x'=>x''-2x'-3x=0\\ \lambda^2-2\lambda-3=0=>\lambda=3\;\;\;\;\;\;\;\lambda=-1=>x=C_1e^{3t}+C_2e^{-t}=>x'=3C_1e^{3t}-C_2e^{-t}\\ y=C_1e^{3t}+C_2e^{-t}-3C_1e^{3t}+C_2e^{-t}=-2C_1e^{3t}+2C_2e^{-t}" align="absmiddle" class="latex-formula">