Serway & Jewett — Physics and Measurement: Problem 39

A woman stands at a horizontal distance \( x \) from a mountain and measures the angle of elevation of the mountaintop above the horizontal as \( \theta \). After walking a distance \( d \) closer to the mountain on level ground, she finds the angle to be \( \phi \). Find a general equation for the height \( y \) of the mountain in terms of \( d \), \( \phi \), and \( \theta \), neglecting the height of her eyes above the ground.