If x and y are positive integers for which 3x + 2y + xy = 115 + 7x, then what is x + y?
Hello Guest,
here's the answer:
\(3x+2y+xy=115+7x\) ,
\(\frac{d}{dx}(3x)+\frac{d}{dx}(2y)+\frac{d}{dx}(xy)=\frac{d}{dx}(115)+\frac{d}{dx}(7x)\),
\(3+\frac{d}{dx}(2y)+\frac{d}{dx}(xy)=\frac{d}{dx}(115)+\frac{d}{dx}(7x)\),
\(3+\frac{d}{dy}(2y)*\frac{dy}{dx}+\frac{d}{dx}(xy)=\frac{d}{dx}(115)+\frac{d}{dx}(7x)\) ,
\(3+\frac{d}{dy}(2y)*\frac{dy}{dx}+\frac{d}{dx}(x)*y+x*\frac{d}{dx}(y)=\frac{d}{dx}(115)+\frac{d}{dx}(7x)\) ,
\(3+\frac{d}{dy}(2y)*\frac{dy}{dx}+\frac{d}{dx}(x)*y+x*\frac{d}{dx}(y)=0+\frac{d}{dx}(7x)\) ,
\(3+2*\frac{dy}{dx}+\frac{d}{dx}(x)*y+x*\frac{d}{dx}(y)=0+\frac{d}{dx}(7x)\) ,
\(3+2*\frac{dy}{dx}+1y+x*\frac{d}{dx}(y)=0+\frac{d}{dx}(7x)\) ,
\(3+2*\frac{dy}{dx}+1y+x*\frac{d}{dx}(y)=0+\frac{d}{dx}(7x)\) ,
\(3+2*\frac{dy}{dx}+1y+x*\frac{d}{dy}(y)*\frac{dy}{dx}=0+\frac{d}{dx}(7x)\) ,
\(3+2*\frac{dy}{dx}+1y+x*\frac{d}{dy}(y)*\frac{dy}{dx}=\frac{d}{dx}(7x)\) ,
\(3+2*\frac{dy}{dx}+1y+x*\frac{d}{dy}(y)*\frac{dy}{dx}=7\) ,
\(3+2*\frac{dy}{dx}+y+x*\frac{d}{dy}(y)*\frac{dy}{dx}=7\) ,
\(3+2*\frac{dy}{dx}+y+x*1*\frac{dy}{dx}=7\) ,
\(3+2*\frac{dy}{dx}+y+x*\frac{dy}{dx}=7\) ,
\(2*\frac{dy}{dx}+x*\frac{dy}{dx}=7-3-y\) ,
\((2+x)*\frac{dy}{dx}=7-3-y\) ,
\((2+x)*\frac{dy}{dx}=4-y\) ,
\(\frac{dy}{dx}=\frac{4-y}{2+x}\) ,
so the solution is: \(\frac{dy}{dx}=\frac{4-y}{2+x}\) .
Straight