Question 1021391
Dividing by a fraction is equivalent to multiplying by its reciprocal.
{{{((x^2-81)/(x^2-20x+100))/((x+9)/(x-10))=((x^2-81)/(x^2-20x+100))*((x-10)/(x+9))}}}
{{{((x^2-81)/(x^2-20x+100))/((x+9)/(x-10))=(((x-9)(x+9))/(x-10)^2)*((x-10)/(x+9))}}}
{{{((x^2-81)/(x^2-20x+100))/((x+9)/(x-10))=highlight((x-9)/(x-10))}}}