\[\left(\int_{a}^{b}(f(x)+g(x))^{p}\,\mathrm{d}x\right)^{1/p}\leq\left(\int_{a}^%
{b}(f(x))^{p}\,\mathrm{d}x\right)^{1/p}+\left(\int_{a}^{b}(g(x))^{p}\,\mathrm{%
d}x\right)^{1/p}.\]