This is LaTeX code:

[latex]
 
g\left(c\right)\left[\underline{f\left(x\right)-f\left(c\right)-\mathrm{D}f\left(c\right)\left(x-c\right)}\right]+\left[\underline{g\left(x\right)-g\left(c\right)-\mathrm{D}g\left(c\right)\left(x-c\right)}\right]f\left(c\right)+\left[\underline{g\left(x\right)-g\left(c\right)}\right]\left[\underline{f\left(x\right)-f\left(c\right)}\right]
 
[/latex]