Question 179777
{{{r/(r-1) + r/(r-9)=1}}}

{{{(r(r-1)(r-9))/(r-1) + (r(r-1)(r-9))/(r-9)=(r-1)(r-9)}}}
{{{r(r-9) + r(r-1)=r^2-10r+9}}}
{{{r^2-9r + r^2-r=r^2-10r+9}}}
{{{2r^2-10r=r^2-10r+9}}}
{{{r^2-9=0}}}
{{{(r-3)(r+3)=0}}}
Two solutions : r=-3, 3
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{{{d/(d+4) + d/(d+9)=1}}}
{{{(d(d+4)(d+9))/(d+4) + (d(d+4)(d+9))/(d+9)=(d+4)(d+9)}}}
{{{d(d+9) + d(d+4)=d^2+13d+36}}}
{{{d^2+9d + d^2+4d=d^2+13d+36}}}
{{{2d^2+13d=d^2+13d+36}}}
{{{d^2-36=0}}}
{{{(d-6)(d+6)=0}}}
Two solutions : d=-6, 6