Because of the length of the advertisement. BC is the two real roots of the equation x 2-35x+300 = 0.
So AD or BC = 15 or 20;
Cross d to make CB a parallel line, and cross AB to e.
∠A+∠B=90 degrees, so AED is a right triangle with hypotenuse AE = 25.
Triangle AED area = 0.5 *15 * 20 =150;
So do = 150 * 2/AE = 12.
1.
Trapezoidal area = parallelogram area EBCD+ triangular area AED
=CD*DO+ 150= 198
2.
When AD=20, BC =15;
ob=4+( 15^2- 12^2)^0.5=7
The analytical formula of straight line BC is y=k(x-7), because point C (4 12) is on straight line BC, and k =-4;
The analytical formula of BC line is y=-4(x-7).
When AD= 15, BC = 20.
OB=4+(20^2- 12^2)^0.5=20
The analytical formula of straight line BC is y=k(x-20), because point C (4 12) is on straight line BC, and k =-3/4;
The analytical formula of BC line is y=-3(x-20)/4.
3.
Because ∠ ADE = 90 degrees, ∠ ADO = ∠ CDE.
To make △PCD similar to △AOD, only ∠ DPC = 90 degrees or ∠ DCP = 90 degrees is needed.
As shown in the figure, we can get two points, P 1 and P2.
According to BC's analytical formula, it is easy to get the analytical formula of straight line DE.
1) When the analytical formula of the straight line BC is y=-4(x-7),
& lt 1 & gt； When DPC = 90 degrees.
The analytical formula of straight line DE is y=-4x+ 12? ( 1)
CP 1 is perpendicular to DE and passes through point (4, 12).
Therefore, the analytical formula of the straight line CP 1 is y = (x-4)/4+12 = x/4+1(2).
The coordinates of Lian Li (1)(2)p 1 are (4/ 17, 188/ 17).
& lt2> when < DCP = 90 degrees.
Because the abscissas of P2 and C are the same, on DE, it is obtained according to (1).
P2 point coordinates (4, -4)
2) When the analytical formula of BC line is y=-3(x-20)/4.
& lt 1 & gt； When DPC = 90 degrees.
The analytical formula of straight line DE is y=-3x/4+ 12? ( 1)
CP 1 is perpendicular to DE and passes through point (4, 12).
So the analytical formula of the straight line CP 1 is y=4(x-4)/3+ 12=4x/3+20/3? (2)
The coordinates of Lian Li (1)(2)p 1 are (64/25, 252/25).
& lt2> when < DCP = 90 degrees.
Because the abscissas of P2 and C are the same, on DE, it is obtained according to (1).
P2 point coordinates (4, 9)