The linear approximation you found using y=cosx at a =pi can be used to find cos(pi+0.05). What is cos(pi+o.o5) equal to?
I found -1 for the approximation of y=cos(x) at a=pi, but how would I find cos(pi+0.05)?
since y = -1 is the linear approximation, your estimate would be cos(π+0.05) ≈ -1
In fact, it is -0.9987 which is pretty close.