Question 327205
{{{(a+3)/(a^2-a-2)-(a-4)/(a^2-2a-3)=(a+3)/((a-2)(a+1))-(a-4)/((a-3)(a+1))}}}
Use a common denominator, {{{(a-2)(a+1)(a-3)}}}
{{{(a+3)/(a^2-a-2)-(a-4)/(a^2-2a-3)=((a+3)(a-3))/((a-2)(a+1)(a-3))-((a-4)(a-2))/((a-2)(a-3)(a+1))}}}

{{{(a+3)/(a^2-a-2)-(a-4)/(a^2-2a-3)=(a^2-9)/((a-3)(a-2)(a+1))-(a^2-6a+8)/((a-3)(a-2)(a+1))}}}
{{{(a+3)/(a^2-a-2)-(a-4)/(a^2-2a-3)=(a^2-9-(a^2-6a+8))/((a-3)(a-2)(a+1))}}}

{{{(a+3)/(a^2-a-2)-(a-4)/(a^2-2a-3)=(a^2-9-a^2+6a-8)/((a-2)(a-3)(a+1))}}}
{{{(a+3)/(a^2-a-2)-(a-4)/(a^2-2a-3)=highlight((6a-17)/((a-2)(a-3)(a+1)))}}}