When two resistors R1 and R2 are connected in parallel, their effective resistance R = (R1R2)/(R1+R2). Show that is R1 and R2 are both increased by a small percentage c, then the percentage increase of R is also c.
The Attempt at a Solution
I had dR1/dt=c and dR2/dt=c. Then dF/dt=∂F/∂R1*dR1/dt + ∂F/∂R2*dR2/dt which I then simplified to c(R1^2+R2^2)/(R1+R2)^2, which does not simplify to c so I clearly did something wrong. Thanks in advance for any help.