A) =(x -9) /(x -3)(x +3) -3/x(3 -x) =
=(x -9)/(x -3)(x +3) +3/x(x -3) =
=(x(x -9) +3(x +3)) /x(x -3)(x +3) =
=(x² -9x +3x +9) /x(x -3)(x +3) =
=(x² -6x +9) /x(x -3)(x +3) =
=(x -3)² /x(x -3)(x+3) =(x -3) /x(x +3)
b) x^3 -8 =(x -2)(x² +2x +4)
=(x² +2x +4 -6x) /(x -2)(x² +2x +4) =
=(x² -4x +4) /(x -2)(x² +2x +4) =
=(x -2)² /(x -2)(x² +2x +4) =
=(x -2) /(x² +2x +4)
в) x² -7x =x(x -7)
=(3(x -7) +21 -x(4 -x)) /x(x -7) =
=(3x -21 +21 -4x +x²) /x(x -7) =
=(x² -x) /x(x -7) =x(x -1) /x(x -7) =(x -1) /(x -7)