Question 1036640
 For all values of the variables for which the expression is defined, perform the indicated operation and express the result in simplest form.
{{{(r^2-7r+10)/(5r-r^2)}}}÷{{{(r^2-4)/(25r^3)}}}
invert the dividing fraction and multiply
{{{(r^2-7r+10)/(5r-r^2)}}}*{{{(25r^3)/(r^2-4)}}} 
Factor
{{{((r-2)(r-5))/(r(5-r))}}}*{{{(25r^3)/((r-2)(r+2))}}}
Factor out -1 so we can cancel the (r-5)
{{{((r-2)(r-5))/(-1r(r-5))}}}*{{{(25r^3)/((r-2)(r+2))}}}
Cancel -r, (r-5), (r-2), you are left with
{{{(-25r^2)/((r+2))}}}