y=(5+x)/(x-7)
y'=(5+x)'*(x-7)-(5+x)*(x-7)'/(x-7)^2
y'=(x-7)-(5+x)/(x-7)^2
y'=(x-7-5-x)/(x-7)^2
y'=-12/(x-7)^2
y=(5+x)/(x-7)
По правилу производная дроби
y " =((5+x)(x-7) " = ((5+x) ' *(x-7) - (5+x)*(x-7) ' )/(x-7)^2 = ((1*(x-7) -1*(x+5))/(x-7)^2 =
=(x-7-x-5)/(x-7)^2 = -12)/(x-7)^2
