人生一线牵出了万般需能F =
F 1+F 2+2F 1F 2cos θa =
b +c -2bc ⋅cos A 2
2
2
2
2
tan θ=
F 2sin αF 1+F 2cos α
2
∴F =
(F 1+F 2cos α) +(F 2sin α)
2
=
F 1+F 2+2F 1F 2cos α22
F 1sin α1
=
F 2sin α2
=
F 3sin α3
a sin A
=
b sin B
=
c sin C
=2R R ∆ABC
∠1=∠2, ∠3=∠OF 1F 2⇒sin α1=sin(180 -α1) =sin ∠1=sin ∠2sin α2=sin F 1OF 2; sin α3=sin ∠3=sin OF 1F 2∴
F 1s i n ∠2
=
F 2
s i n ∠F 1OF 2
'
'
' '
=
F 3
s i n ∠OF 1F 2
'
e =
c a
(x -a ) 2+(y -b ) 2=r 2O (a , b ) x a
22
+
y b
22
=1, (a >b >0) F 1(-c , 0), F 2(c , 0) 22
x a
22
-
y b
=1, (c >a >0, b
p 2
2
=c -a ) F 1(-c , 0), F 2(c , 0) 22
y =2px , (p >0) F (2
, 0)
F =-kx , [k =
mg l
]l x F x k m g l G G 1=mg sin θF F =G 1=mg s i n θθsin θ≈θ≈
x l
F =-
mg l
x
人生一线牵出了万般需能F =
F 1+F 2+2F 1F 2cos θa =
b +c -2bc ⋅cos A 2
2
2
2
2
tan θ=
F 2sin αF 1+F 2cos α
2
∴F =
(F 1+F 2cos α) +(F 2sin α)
2
=
F 1+F 2+2F 1F 2cos α22
F 1sin α1
=
F 2sin α2
=
F 3sin α3
a sin A
=
b sin B
=
c sin C
=2R R ∆ABC
∠1=∠2, ∠3=∠OF 1F 2⇒sin α1=sin(180 -α1) =sin ∠1=sin ∠2sin α2=sin F 1OF 2; sin α3=sin ∠3=sin OF 1F 2∴
F 1s i n ∠2
=
F 2
s i n ∠F 1OF 2
'
'
' '
=
F 3
s i n ∠OF 1F 2
'
e =
c a
(x -a ) 2+(y -b ) 2=r 2O (a , b ) x a
22
+
y b
22
=1, (a >b >0) F 1(-c , 0), F 2(c , 0) 22
x a
22
-
y b
=1, (c >a >0, b
p 2
2
=c -a ) F 1(-c , 0), F 2(c , 0) 22
y =2px , (p >0) F (2
, 0)
F =-kx , [k =
mg l
]l x F x k m g l G G 1=mg sin θF F =G 1=mg s i n θθsin θ≈θ≈
x l
F =-
mg l
x