Thread: angles between two lines

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?

Originally Posted by ling_c_0202

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?

The solutions to,

Are,



Thus,


The angle between two (non-perpendicular) lines is,

Thus,

Thus,

Exactly the same as what I 've done. Thanks!