Hoe breed is de rivier?

$\eqalign{ & \frac{h} {{\tan (60)}} + \frac{h} {{\tan (40)}} = 120 \cr & \frac{{\tan (40) \cdot h}} {{\tan (60) \cdot \tan (40)}} + \frac{{\tan (60) \cdot h}} {{\tan (60) \cdot \tan (40)}} = 120 \cr & \frac{{\tan (40) \cdot h + \tan (60) \cdot h}} {{\tan (60) \cdot \tan (40)}} = 120 \cr & \frac{{\left( {\tan (40) + \tan (60)} \right) \cdot h}} {{\tan (60) \cdot \tan (40)}} = 120 \cr & \left( {\tan (40) + \tan (60)} \right) \cdot h = 120 \cdot \tan (60) \cdot \tan (40) \cr & {\text{h = }}\frac{{120 \cdot \tan (60) \cdot \tan (40)}} {{\tan (40) + \tan (60)}} \approx 67,8 \cr}$

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• hoe breed is de rivier?