Graphs reveal area secrets through simple shapes.
The constant function f(x)=a spanning 0 to xโ encloses a rectangle of area a๐ฅโ. The linear function f(x)=a๐ฅ encloses a triangle of area a๐ฅโยฒ/2. These equal the evaluated definite integrals of each.
Spring manufacturers compute elastic potential energy as the triangular area under the force-extension graph, yielding ยฝkxยฒ for a spring constant k.