7. 4 2 cos (arccos 1/8) + 3 cos (arccos 5/12)

1) $$cos(arccos(\frac{1}{8})) = \frac{1}{8}$$

2) $$cos(arccos(\frac{5}{12})) = \frac{5}{12}$$

3) $$2 \cdot \frac{1}{8} = \frac{1}{4}$$

4) $$3 \cdot \frac{5}{12} = \frac{5}{4}$$

5) $$\frac{1}{4} + \frac{5}{4} = \frac{6}{4} = \frac{3}{2} = 1.5$$

Ответ: 1.5