Nếu $\int\limits_0^1 {f\left( x \right){\mkern 1mu} {\rm{d}}x} = 5$ và $\int\limits_1^2 {f\left( x \right){\mkern 1mu} {\rm{d}}x} = 2$ thì $\int\limits_0^2 {f\left( x \right){\mkern 1mu} {\rm{d}}x} $ bằng