Ответ:

Объяснение:

(a+5)/(a-5) +20a/(25-a²)=(a+5)/(a-5) -20a/((a-5)(a+5))=((a+5)(a+5)-20a)/((a-5)(a+5))=(a²+5a-5a-25-20a)/((a-5)(a+5))=(a²-20a-25)/(a²-25)

2x/(x²-6x+9) -(2x+12)/(x²-9)=2x/(x-3)² -(2x+12)/((x-3)(x+3))=(2x(x+3)-2(x+6)(x-3))/((x-3)²(x+3))=2(x²+3x-x²+3x-6x+18)/((x²-6x+9)(x+3))=2·18/(x³-6x²+9x+3x²-18x+27)=36/(x³-3x²-9x+27)

6a/(a-7) -21/(a+7)+6a²/(49-a²)=(6a(a+7)-21(a-7))/((a-7)(a+7)) -6a²/(a²-49)=(6a²+42a-21a+147-6a²)/(a²-49)=(21a+147)/(a²-49)

(3b-1)/(6b+2) -6b/(1-9b²) -(3b+1)/(9b-3)=(3b-1)/(2(3b+1)) +6b/((3b-1)(3b+1)) -(3b+1)/(3(3b-1))=(3(3b-1)²+36b-2(3b+1)²)/(6(3b-1)(3b+1))=(3(9b²-6b+1)+36b-2(9b²+6b+1))/(6(3b-1)(3b+1))=(27b²-18b+3+36b-18b²-12b-2)/(6(3b-1)(3b+1))=(9b²+6b+1)/(6(3b-1)(3b+1))=(3b+1)²/(6(3b-1)(3b+1))=(3b+1)/(18b-6)