1、与面积的关系
S ∆ABC =
S ∆ABC
S ∆ABC 111ab sin C =bc sin A =ca sin B 222abc ==2R 2sin A sin B sin C 4R =pr =(p -a ) r a =(p -b ) r b =(p -c ) r c
p (p -a )(p -b )(p -c ) =rr a r b r c S ∆ABC =
2、三角表示
A B C p =4R cos cos cos 222
A B C r =4R sin sin sin 222
A B C p -a =4R cos sin sin 222 A B C r a =4R sin cos cos 222
B C AI =4R sin sin 22
B C AI a =4R cos cos 22
3、几个恒等式
p -a p -b p -c ++=1p p p
r r r 1111++=1(++=) r a r b r c r a r b r c r AI BI CI ++=1AI a BI b CI c
1、与面积的关系
S ∆ABC =
S ∆ABC
S ∆ABC 111ab sin C =bc sin A =ca sin B 222abc ==2R 2sin A sin B sin C 4R =pr =(p -a ) r a =(p -b ) r b =(p -c ) r c
p (p -a )(p -b )(p -c ) =rr a r b r c S ∆ABC =
2、三角表示
A B C p =4R cos cos cos 222
A B C r =4R sin sin sin 222
A B C p -a =4R cos sin sin 222 A B C r a =4R sin cos cos 222
B C AI =4R sin sin 22
B C AI a =4R cos cos 22
3、几个恒等式
p -a p -b p -c ++=1p p p
r r r 1111++=1(++=) r a r b r c r a r b r c r AI BI CI ++=1AI a BI b CI c