№1 a) (2a/51x^2y)* (17x^3y/2a^2)= 2a*17x^3y/ 51x^2y*2a^2=x/3a

б) (x+2/x-1)*(x^2-1/x^2-4)= (x+2)*(x-1)(x+1)/ (x-1)* (x-2)(x+2)=x+1/x-2

в) (24b^2c/3a^3)÷ (16bc/a^2)= (24b^2c*a^2)/ 3a^3*16bc= b/2a

№2 (y+c)/с *(c/y- c/y+с)=(y+c*c/сy) -( y+c*c/с(y+c))= (y+c)/с- 1

№4 (4/(x-2)(x+2)+1/x-2)* (x+2)^2/3= 4/(x-2)(x+2)*(x+2)^2/3))+(1*(x+2)^2)/(x-2)*3=(4x+8+x^2+4x+4)/3x-6=(8x+x^2+12)/3x-6