T 15: draw a standard drawing, cut it with compasses and discuss it in categories.

When CD=DB', a solution is found, and DB' is decisive = 16.

When CB'=B'D and b' is on the vertical line of CD, let B'G⊥AB, B'H⊥CD, then because EB'= 13, EG= 13-8=5, b' g = 65438.

Because HD=8, B'D=4, root number 5.

When CB'=CD, F falls right on C.

To sum up, this space should be filled with 16 or four radicals 5.

T23: The picture of the above question can be said directly. . .

( 1)y=- 1/8x？ The process of +8 is abbreviated.

(2) The guess that looks so cute is actually correct.

Let p (x,-1/8x 2+8), then PD = (1/64x4+1/2x2+4) (distance formula between two points) = 1/8x 2+2. And pf = 1/8x 2, so PD-PF=2 is a constant value.

(3) Continue to set p (x,-1/8x 2+8), and use X to represent the PDE area of the triangle with the formula of horizontal width and vertical height.

S =- 1/4x 2-3x+4 (-8

This small problem can also be deduced by parallel lines and the tangent position can be found by delta method.

What is the smallest circumference? Sorry, this one uses a calculator, and the circumference is the smallest when P (-4,6).

Therefore, the point *** 1 1 P (the exact area integer with the smallest perimeter) has the smallest perimeter at p (-4,6).

The way to find the last small question and the last small question. . .