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@@ -11,6 +11,10 @@
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;; SAS -- Law of Cosines
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;; SSS -- Law of Cosines
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+(defun between-p (lower number upper)
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+ (and (>= number lower)
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+ (<= number upper)))
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+
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(defun solve-asa (anglea sidea angleb)
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"Solve a ASA triangle using the method of sines. Angles assumed to be in degrees."
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(let* ((anglec (- 180 anglea angleb))
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@@ -29,20 +33,35 @@
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(defun solve-ssa (sidea sideb anglea)
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"Solve an SSA triangle using the method of sines. Angles are assumed to be in degrees."
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- (let ((angleb (asin (/ (* sideb (sin anglea))
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- sidea))))
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- (cond
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- ((< 1 angleb) nil)
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- (())))
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- (let* ((angleb (asin (/ (* sideb (sin anglea))
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- sidea)))
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- (anglec (- 180 anglea angleb))
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- (sidec (/ (* (sin anglec)
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- sidea)
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- (sin anglea))))
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- (list :angle-a anglea
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- :angle-b angleb
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- :angle-c anglec
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- :side-a sidea
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- :side-b sideb
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- :side-c sidec)))
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+ (let ((sinb (/ (* sideb (sin anglea))
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+ sidea)))
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+ (if (between-p -1 sinb 1)
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+ (let* ((angleb (asin sinb))
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+ (anglec (- 180 anglea angleb))
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+ (sidec (asin (/ (* (sin anglec) sidea)
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+ (sin anglea)))))
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+ (if (< (+ anglea angleb))
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+ (let* ((angleb-prime (- 180 angleb))
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+ (anglec-prime (- 180 anglea angleb-prime))
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+ (sidec-prime (/ (* (sin anglec-prime) sidea)
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+ (sin anglea))))
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+ (values (list :angle-a anglea
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+ :angle-b angleb
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+ :angle-c anglec
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+ :side-a sidea
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+ :side-b sideb
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+ :sidec sidec)
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+ (list :angle-a anglea
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+ :angle-b angleb-prime
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+ :angle-c anglec-prime
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+ :sidea sidea
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+ :sideb sideb
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+ :sidec sidec-prime)))
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+ (values (list :angle-a anglea
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+ :angle-b angleb
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+ :angle-c anglec
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+ :side-a sidea
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+ :side-b sideb
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+ :sidec sidec)
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+ nil)))
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+ (values nil nil))))
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