Sagot :
[tex]x\cdot y=36\ \ \ and\ \ \ x+y=7\\\\y=7-x\ \ \ \Rightarrow\ \ \ x(7-x)=36\\\\7x-x^2=36\\\\-x^2+7x-36=0\ \ \ \Rightarrow\ \ \ \Delta=7^2-4\cdot(-1)\cdot(-36)=49-144=-95\\\\\Delta<0\ \ \ \Rightarrow\ \ \ not\ exist\ real\ solution[/tex]