#2/(x-3)+5/(x-4)=3/(x^2-7x+12)#
#:.2/(x-3)+5/(x-4)=3/((x-3)(x-4))#
#:.(2(x-4)+5(x-3)=3)/((x-3)(x-4))#
multiply both sides by #(x-3)(x-4)#
#:.2(x-4)+5(x-3)=3#
#:.2x-8+5x-15=3#
#:.7x-23=3#
#:.7x=3+23#
#:.7x=26#
#:.color(magenta)(x=26/7#
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check:
#:.2/((color(magenta)(26/7))-3)+5/((color(magenta)(26/7))-4)=3/((color(magenta)(26/7))^2-7(color(magenta)(26/7))+12)#
#:.2/(26/7-21/7)+5/(26/7-28/7)=3/((676/49)-26+12)#
#:.2/(5/7)+5/(-2/7)=3/((676/49)-14)#
#:.(2/1 xx 7/5)+(5/1 xx -7/2)=3/(676/49-686/49)#
#:.14/5-35/2=3/(-10/49)#
#:.14/5-35/2=3/1 xx -49/10#
#:.14/5-35/2=-147/10#
#:.(2(14)-5(35)=-147)/10#
multiply both sides by #10#
#:.2(14)-5(35)=-147#
#:.28-175=-147#
#:.color(magenta)(-147=-147#