設(shè)AB直線為y=kx+b
k=tan30=√3/3
y=√3x/3+b
x=0,y=b
x^2+(y-b)^2=25
x^2+y^2=4
2by=-21 y=-21/2b
x^2=4-21^2/4b^2
y=0,x=-b√3
(x+b√3)^2+y^2=3
x^2+y^2=4
2bx√3=-1
x=√3/(6b)
x^2=1/(12b^2)
4-21^2/4b^2=1/12b^2
16b^2=21^2*3+1
b=-√(1324/16)=-√1324/4
BC=√1324/4,AC=√3972/4
Sabc=ACBC/2=1324√3/32