I see on book : $t_{0.025,59}$ = 2.009 But when call qt in R. We have this result:
qt(0.025,59) [1] -2.000995
I don't know why have different in here.
As I think, $t_{0.025,59}$ must is negative . Because it belongs left tail of distribution.
Anyone know clearly about this. Please help me.
The difference is likely due to a lack of care in being explicit. R gives the correct value.
I can only make guesses as to why your book has what it does. Some books I've seen use a context-dependent interpretation of the test statistic. For example, when some books are talking about a right-tailed hypothesis test, they might write:
$$t_{\alpha,df}$$
instead of the correct right-tailed test:
$$t_{1 -\alpha,df}$$
This isn't correct to do, and it's really sloppy, but it's a habit even I get into. I know that the z-value for p = 0.025 in the tails is 1.96. In my head, I have the association:
$$z_{\alpha=0.025} = 1.96$$
I correct the sign depending on the context, but I recall it in a not technically-correct manner. I suspect that your book might have done the same.