# A string theory

Suppose a piece of string is drawn taut between two endposts, and let $$\phi(x,t)$$ denote the height of the string above the line connecting the endposts at the point $$x$$ along the same line at time $$t$$. Which of the following differential equations correctly describes the evolution of the string shape over time?

Assumptions

• The composition of the string is uniform.
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