ahora le daremos solucion al ejercicio de la imagen 

1.-\(\frac{1}{rea}=\frac{1}{r}+\frac{1}{\Sigma4}=\frac{3r+r}{3r^2}=\frac{4r}{3r}=\frac{4}{3r}=req=\frac{3r}{4}\)

2.-\(r+r+req=2r+\frac{3}{4}r\)

3.-\(\frac{1}{req}=\frac{1}{r}+\frac{1}{2r+req}=\frac{2r+\frac{3}{4}r+r}{r\left(2r+\frac{3}{4}r\right)}=\frac{\frac{15}{4}r}{r\left(\frac{11}{4}r\right)}\)