20/12/21 00:24:42.41 bRUvkX+j.net
fn <- function(){
ABC=runif(1,0,pi/2) # ∠ABC,∠DCBは0~90°から乱数で選ぶ
DCB=runif(1,0,pi/2)
# ABC=pi/180*80
# DCB=pi/180*45
L8=8 # ADの長さ
L14=14 # BCの長さ
S3=3
S8=8
rS=(S3+S8)/(S8) # 台形ABCD,台形PBCQの面積比 11/8
AD2S <- function(AD=L8,BC=L14,b=ABC,c=DCB,print=F){
# AB : y = tan(b)*x
# DC : y = tan(pi-c)*(x-BC) = -tan(c)*(x-BC)
# A(a1,tan(b)*a1)
# tan(b)*a1=-tan(c)*( a1+AD -BC)
a1 = tan(c)*(BC-AD)/(tan(b)+tan(c))
A=a1+1i*tan(b)*a1
B=0i
C=BC+0i
D=a1+AD + 1i*tan(b)*a1
if(print){ plot(NULL,xlim=c(0,L14),ylim=c(0,Im(A)), asp=1,ann=F,bty='n',axes=F) ; axis(1)
B=0i;C=L14+0i;pt(B,'B');pt(C,'C');seg(B,C)
a1 = tan(c)*(L14-L8)/(tan(ABC)+tan(DCB))
A=a1+1i*a1*tan(ABC);pt(A,'A');seg(A,B)
CD0=1i*(0-L14)*tan(pi-DCB)
D=intsect(C,CD0,A,A+1)
pt(D,'D');seg(D,C);seg(A,D)}
ABC2S(A,B,C)+ABC2S(A,D,C)
}