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(\mathrm{b}-\mathrm{a}) \cdot(\max \text { of } \mathrm{f} \text { on }[\mathrm{a}, \mathrm{b}])=(4)(9)=36: 8 \leq \int_{1}^{5} \mathrm{f}(x) \mathrm{d} \mathrm{x} \leq 36