Respuesta :

[tex]a+3=\dfrac{2a+7}{r}\\ r(a+3)=2a+7\\ ar+3r=2a+7\\ ar-2a=7-3r\\ a(r-2)=7-3r\\ a=\dfrac{7-3r}{r-2}\\ a=-\dfrac{3r-7}{r-2} [/tex]