Hello, I'm having trouble with this maths question and was wondering if someone could help me?? The question asks: The electrical resistance R of a wire is given by k / r^2 where k = constant, r = radius of wire. Use differentials to estimate the percentage error in the measured value of r if we want the percentage error in R to be within +/- 3%. I'm really not sure if this is the right approach... please help me... Using the method of linear approx. i have... ΔR = R(r + Δr) - R(r) ~ (dR(r) / dr) * ( Δr ) I know... R = k / r^2 dR/dr = -2*k*( r^-3 ) and therefore... ΔR = -2*k*( r^-3 ) * ( Δr ) So i'm thinking to increase R by 3% i need... ΔR / R(r) = 0.03 but after substituting everything in i get Δr = 0.03?? please i really need help!!