;***********************************************
;	三角形　                                
;***********************************************
(defun c:triangle()
  (prompt "\n3辺を入力（反時計廻り）")
  (setq gp1 (getpoint "\n三角形の底辺 1点目 <Enter=終了> :"))
	(if (/= gp1 nil)
	  (progn
	      (setq gp2 (getpoint "\n底辺の2点目（距離入力でも可）<Enter=終了> :" gp1))
	      (setq distA (distance gp1 gp2 ));a 
		(if (/= gp2 nil);Dist1 Point2
		  (progn
			(setq gl3 (getdist "\n2辺目の長さを入力 <Enter=終了>:" gp2));b 
				(if (/= gl3 nil);Dist2
				  (progn
				    (setq gl4 (getdist "\n3辺目の長さを入力 <Enter=終了>:" gp1));c 
				    	(if (/= gl4 nil);Dist3
					  (progn;p Set
;角度の計算
	;cosB=c2+a2-b2 / 2ca
	(setq cosangB (/ (- (+ (expt gl4 2.0) (expt distA 2.0)) (expt gl3 2.0)) (* 2.0 gl4 distA)))
	(if (< cosangB 1.0);check1
	  (progn
	    (if (> cosangB -1.0);check2
	      (progn
	;cosC=a2+b2-c2 / 2ab
	(setq cosangC (/ (- (+ (expt distA 2.0) (expt gl3 2.0)) (expt gl4 2.0) ) (* 2.0 distA gl3)))
	
	;ARCCOS(X) = -ATN( X / SQRT( -1 * X2 + 1 ) ) + Pi /2=ATAN(1)*4
	(setq angB (+ (* -1.0 (atan( / cosangB (sqrt (+ (* -1 (expt cosangB 2.0)) 1.0))))) (/ (* (atan 1.0) 4.0) 2.0)))
	(setq degB (Radian->Degrees angB))
					  
	(setq angC (+ (* -1.0 (atan( / cosangC (sqrt (+ (* -1 (expt cosangC 2.0)) 1.0))))) (/ (* (atan 1.0) 4.0) 2.0)))
	(setq degC (Radian->Degrees angC))

;点の確認					  
	(setq firstAng (angle gp1 gp2))
	(setq pointC1 (polar gp1 (+ angB firstAng) gl4))
	(setq pointC2 (polar gp2 (- (* (atan 1.0) 4.0) (+ angC firstAng))  gl3))
	

				      		(command "_pline" gp1 gp2 pointC1 "_c" )
				)
	  			(progn
				(prompt "\n余弦定理が成立ちません")
				(princ)
				  )
				    );progn check1 
				   );progn check1
	  			(progn
				(prompt "\n余弦定理が成立ちません")
				(princ)
				  )
	  			);end if check1
				      	);p Set
				  	(progn
				  	(princ)
				  	)
				  	);end if Dist2
			)
			(progn
			(princ)
			)
			);end if Dist3
		   )
		  (progn
		  (princ)
		  )
		  );end if Dist1 Point2
	   )
	  (progn
	  (princ)
	  )
	  );end if Dist1 Point1
  (princ)
  );end defun

(defun Radian->Degrees (nbrOfRadians)

  (* 180.0 (/ nbrOfRadians (* (atan 1.0) 4.0)))

)
(prompt "\ncommand:triangle")
(princ)