If f(x)=(x+1)^2/(2x+1)^3, then f′(1)= −a/b. What is a and b?

f(x) = (x+1)^2/(2x+1)^3

f'(x) = -2(x+1)(x+2)/(2x+1)^4
f'(1) = -2(2)(3)/3^4
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