20 12 detailed answer to the last question of science mathematics in the national volume.

When passing through two points (a 1, b 1), the formula of (a2, b2) is f (x) = (b2-b1)/(a2-a1) * (x-a/kloc-0.

Then PQn passes (Xn+ 1

, 0) point.

That is, (f(Xn)-5)/(Xn-4)(Xn+ 1

-4)+5=0, brought into the calculation are

Xn+ 1=4-5/(xn

+2),

+1 both sides,

Xn+ 1

+ 1

5(xn

+ 1)/(xn

+2), in turn, make yn= 1/(xn

+ 1);

Get 5*

yn+ 1

= 1

yn；

Subtract 5/4 from both sides, there is

5(yn+ 1

- 1/4)=yn

- 1/4;

Yn= 1/(xn+ 1)，y 1- 1/4 = 1/4 = 1/ 12；

yn = 1/ 12 *( 1/5)(n- 1)+ 1/4；

The general formula of xn is

xn=[9-( 1/5)^(n- 1)]/[( 1/5)^(n- 1)+3]； (n=2 can be brought in for checking, and x2 = (44/5)/(16/5) =1/4 satisfies)

Only the second question is written here, but this common term proves that the first question is also indispensable.

The first question is thinking.

4-5/(x+2)>x, at x∈(- 1, 3), is bound to hold, which proves that both sides are sufficient, x < 3, x>2. Get a license.