Question

X sobre y = 3 quartos e X+y =21Qual eh a resposta?

Answer 1

$\begin{cases} \dfrac{x}{y}= \dfrac{3}{4}~~(i)\\\\x+y=21~~(ii) \end{cases}\\\\\\ \boxed{x=21-y}~~em~ii~~(substitua~em~i):\\\\\\ \dfrac{21-y}{y}= \dfrac{3}{4}~~(multiplique~em~cruz):\\\\\\ 4\cdot(21-y)=3\cdot y\\ -4y+84=3y\\ 7y=84\\\\ y= \dfrac{84}{7}\\\\ \Huge\boxed{y=12}~~(substitua~em~i~ou~em~ii):\\\\\\ x+y=21\\ x+12=21\\\\ \Huge\boxed{x=9}$