Hello, landlord! Encounter this kind of question type, a considerable part is the periodicity of the test series, and then understanding! It won't be difficult. Grasp the condition X(n+ 1)=f(X), know that X( 1)=f(Xo) = f (5) = 2, that is, X 1=2, and continue the iteration.

X (2) = f (x1) = f (2) =1,and so on, X3=4, X4=5, X5=2 ... The discovery rule is that the period is 4, that is, X(n)=X(n+4).

Get x (20 10) = x (2) = 1. If you can't work out the basic sequence, try it! You usually find something.

The second question should also be repeated! Knowing that x2 =-1x 3 =1/2x4 =-1/6x5 =1/24, we can't draw a complete conclusion.

xn=(- 1)^(n+ 1)( 1/((n- 1)！ ))。 In addition, if the landlord finds this unconvincing, he can try to prove it by mathematical induction.