PRINT
PRINT "楕円の接線"
PRINT "      Q(x) = ±SQR((a^2*b^2-b^2*xx^2)/a^2)"
PRINT
INPUT PROMPT "長軸の長さ？  ":a2
INPUT PROMPT "短軸の長さ？  ":b2
PRINT
LET a=a2/2
LET b=b2/2
DEF yy1=SQR((a^2*b^2-b^2*xx^2)/a^2)
DEF yy2=-1*SQR((a^2*b^2-b^2*xx^2)/a^2)
DEF f1(x)=(1-(xx/a^2)*x)/(yy1/b^2)    ! 点（x,Q(x)）における楕円の接線方程式
DEF f2(x)=(1-(xx/a^2)*x)/(yy2/b^2)    ! 点（x,Q(x)）における楕円の接線方程式
SET WINDOW -1*a2,a2,-1*a2,a2
FOR xx=-1*a TO a STEP 0.01
   FOR i=-1*a2 TO a2 STEP 0.01
      IF (a^2*b^2-b^2*xx^2)/a^2 = 0 THEN GOTO 10
      PLOT LINES : i,f1(i)
10    NEXT i
   NEXT xx
   PLOT LINES
   FOR xx=-1*a TO a STEP 0.01
      FOR i=-1*a2 TO a2 STEP 0.01
         IF (a^2*b^2-b^2*xx^2)/a^2 = 0 THEN GOTO 20
         PLOT LINES : i,f2(i)
20    NEXT i
   NEXT xx
END