TeX source:

\frac{\mathbf{d} \mathrm{T}(\mathrm{t})}{\mathbf{d} \mathbf{t}}=\frac{\mathbf{d} \mathrm{T}(\mathrm{h}(\mathrm{t}))}{\mathbf{d} \mathrm{h}(\mathrm{t})} \cdot \frac{\mathrm{d} \mathrm{h}(\mathrm{t})}{\mathrm{dt}}=\frac{\mathbf{d} \mathrm{T}(\mathrm{h})}{\mathbf{d} \mathrm{h}} \cdot \frac{\mathrm{d} \mathrm{h}(\mathrm{t})}{\mathrm{dt}}=\frac{-72}{(1+\mathrm{h})^{2}} \cdot(1+\cos (\mathrm{t}))