16.在直角坐标系xOy中,圆O的半径为2,设A(2,0),B(2cosu,2sinu),
BC=3,
所以∠BOC=2arcsin(3/4),C(2cos[u+2arcsin(3/4)],2sin[u+2arcsin(3/4)]),
所以AC^2-AB^2=4{1-cos[u+2arcsin(3/4)]}^2+4{sin[u+2arcsin(3/4)]}^2
-[4(1-cosu)^2+4(sinu)^2]
=-8cos[u+2arcsin(3/4)]+8cosu
=16sin[u+arcsin(3/4)]sin[arcsin(3/4)]
=12sin[u+arcsin(3/4)],
所求的最大值为12.
图示中α是已知角,β是变量。