5/(x-7) - 2/x - 3x/(x² -49) +21/(49-x²) =
= 5/(x-7) - 2/x - [3x/(x-7)(x+7)] - [21/(x-7)(x+7) ]=
= (5x(x+7) - 2(x²-49) - 3x² -21x) / (x(x-7)(x+7) ) =
= (5x²+35x -2x² +98 -3x² -21x) / (x(x-7)(x+7) )=
= (14x +98) / x(x-7)(x+7) =
= 14(x+7) / x(x-7)(x+7) =
= 14 / x(x-7)