B(x) =6/(5x -10) +1 /(3x -6) =6/5(x -2)+1/3(x -2) = (6*3 + 1*5)/ 15(x -2)=23 /15(x-2) ;
B(4) =23/15(4-2)=23/30.
-------------
(a-3) /(a² +3a +9) +9a/(a³ -27) -1/(a-3) = (a-3) /(a² +3a +9) -1/(a-3)+9a/(a³ -3³) =
=( (a-3)² - (a² +3a +9 ) +9a ) / (a-3) /(a² +3a +9) =
(a² - 6a + 9 - a² -3a -9 +9a) / (a-3) /(a² +3a +9) = 0 . * * * a ≠ 3 * * *