10 SCREEN 12
20 WINDOW (-10, 10)-(10, -10)
30 LINE (-5, 3.2)-(3, 3.2)
40 LINE (-5, 3.2)-(0, 6.5)
50 LINE (0, 6.5)-(3, 3.2)
60 LINE (0, 6.5)-(0, 3.2)
70 LOCATE 10, 26
80 PRINT "B"
90 LOCATE 10, 48
100 PRINT "A"
110 LOCATE 8, 28
120 PRINT "a"
130 LOCATE 8, 48
140 PRINT "b"
150 LOCATE 10, 30
160 PRINT "acosB"
170 LOCATE 10, 42
180 PRINT "bcosA"
190 LOCATE 11, 38
200 PRINT "c"
210 LOCATE 7, 39
220 PRINT "C"
230 LOCATE 1, 23
240 PRINT "Proof of the Law of Cosines"
250 PRINT "Prove that c^2=a^2+b^2-2abcosC"
260 LOCATE 12, 1
270 PRINT "c=acosB+bcosA"
280 PRINT "c^2=accosB+bccosA"
290 PRINT "likewise"
300 PRINT "a^2=accosB+abcosC"
310 PRINT "b^2=bccosA+abcosC"
320 PRINT "a^2+b^2=accosB+abcosC+bccosA+abcosC"
330 PRINT "a^2+b^2=[accosB+bccosA]+[abcosC+abcosC]"
340 PRINT "a^2+b^2=c^2+2abcosC"
350 PRINT "So c^2=a^2+b^2-2abcosC"
360 SYSTEM