5. a=30, b=40, C= 6 d-?

По теореме о биссектрисе:

$$\frac{a}{c} = \frac{b}{d}$$

a = 30, b = 40, c = 6

$$\frac{30}{6} = \frac{40}{d}$$ $$d = \frac{40 \cdot 6}{30} = \frac{240}{30} = 8$$

Ответ: d = 8