Помогите решить задания пожалуйста

Ответ:

Объяснение:

a)

[(a+3)/(a-3) + (a-3)/(a+3)]  : (3a²+27)/(9a-a²)=

=[(a+3)²+(a-3)²)/(a²-9) ] * -a(a-9) / 3(a²+9)=

=(a²+6a+9+a²-6a+9)/(a²-9)  *  -(a²-9)/3(a²+9)=

=(2a²+18)/(a²-9)  *  -a(a-9)/3(a²+9) = 2(a²+9)/(a²-9) *(a²-9)/3(a²+9)=-2/3

b)

[5x  -10x/(x+1)]:(15x-15)/4x+4)= [(5x(x+1)-10x]/(x+1) : 15(x-1)/4(x+1)=

=(5x²+5x-10x)/(x+1) * 4(x+1)/15(x-1)=(5x²-5x)/(x+1) *4(x+1)/15(x-1)=

=5x(x-1) * 4/15(x-1)=20x/15=4x/3

c)

(3a/(a-4)  - (a+2)/(5a-20) * 240/(a²+2a)=

=3a/(a-4)  - (a+2)/5(a-4) *240/a²+2a) =3a/(a-4) - (240(a+2)/5a(a-4)(a+2)=

=(15a²-240)/5a(a-4)=15(a²-16)/5a(a-4)= 15(a-4)(a+4)/5a(a-4) =3(a+4)/a