... 11 312 2 2123 123 330akbaaaakbbbbbbbakb,(,,)ì=ïÛ=Û==¹íï=î · 1122 33abababab =++rr· 1122 330abababab^Û++=rr·2222 123 aaaa=++r· 222 122 aaaa=++r · 1122 33222222 123 123ababababababaaabbb.cos(,)..++==++++rrrrrr(với ... DABC. T ú suy ra di ng cao AH ca DABC.a) 123 03 7125 0ABC(;;),(;;),(;;)-b)01321 1123 171019ABC(;;),(;;),(;;)-c)34753 2123 ABC(;;),(;;),(;;) d)423211387ABC(;;),(;;),(;;) e) 3121 21113ABC(;;),(;;),(;;) ... 12 32231442 412 xtxtdytdytztzt':,:''ìì=-=+ïï=+=-ííïï=-+=-îîb) 12 1223 312 2344xtxtdytdytztzt':,:''ìì=+=-+ïï=-+=+ííïï=+=-+îîc) 12 22113 312 xtxtdytdytztzt':,:''ìì=+=+ïï=+=+ííïï=-=+îîd)...