University Calculus: Early Transcendentals (3rd Edition)

The change in the angle of elevation when a 4% error occurs is less than 0.01 radians ($\approx0.57^\circ$) from $75^\circ$
The given height of the building is h and the distance from the point on the ground is 30 ft. change in height(dh): $\frac{dh}{h}$ is less than 4% $\theta =75^\circ$ angle of elevation so $h=30\tan\theta$ so $\frac{dh}{h}=\frac{30\sec^2{\theta}d\theta}{30\tan\theta}$ $0.04\lt\frac{30\sec^2{75}d\theta}{30\tan75}$ $0.01\lt d\theta$