Câu 13:
Biết ∫23f(x)dx=6.\int\limits_{2}^{3}{f\left( x \right)\text{d}x}=6.2∫3f(x)dx=6. Khi đó ∫2312f(x)dx\int\limits_{2}^{3}{\frac{1}{2}f\left( x \right)\text{d}x}2∫321f(x)dx bằng
