Happy New Year!

There is a question on my exercise book that:

The slopes of lines L1 and L2 are the roots of the equation 6 x^2 - 5x - 1 = 0

If a is the acute angle between L1 and L2, find the value of tan a .

The answer I 've calculated is 7 / 5.

But the book says that it should be 1/7.

How can I get this or it's the mistake of the book?