Question

se stie ca 7a+3b=29 si a+b=7 aflati a si b

Answer 1

$\displaystyle 7a+3b=29 \\ a+b=7 \\ a,b=? \\ a+b=7 \Rightarrow a=7-b \\ 7a+3b=29 \Rightarrow 7(7-b)+3b=29 \Rightarrow 49-7b+3b=29\Rightarrow \\ ~~~~~~~~~~~~~~~~~~~~~~~ \Rightarrow -7b+3b=29-49 \Rightarrow -4b=-20\Rightarrow \\ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ \Rightarrow b= \frac{-20}{-4} \Rightarrow \boxed{b=5} \\ a=7-b \Rightarrow a=7-5 \Rightarrow \boxed{a=2}$

Answer 2

[tex]a+b=7\\7a+3b=29\\4a+3a+3b=29\\Dam.factor.comun.pe.3:\\4a+3*(a+b)=29\\4a+3*7=29\\4a+21=29\\ 4a=29-21\\4a=8\\a=\frac{8}{4}\\a=2\\2+b=7\\b=7-2\\b=5\\ Proba:\\2*7+5*3=14+15=29(Adevarat)\\2+5=7(Adevarat)\\Sfarsit![/tex]