Why is tangent negative in the second quadrant?

The tangent function is the ratio of "opposite side" to "adjacent side."  It so happens that the "adjacent side" is negative in Quadrants II and III, whereas the "opposite side" is positive.  A positive quantity divided by a negative one produces a negative result; hence, the tangent function is negative in Quadrant II.

first, let's see what the pattern is.

58 - x = 47

46 - x = 36

x = 9

so this means that the term after 25 is 25 - 9:

the next term in the sequence is 16.