(1)向量AB·向量AC
=(1+tanx)*sin(x-45)+(1-tanx)*sin(x+45)
=(1+tanx)(sinx-cosx)/根号2+(1-tanx)(sinx+cosx)/根号2
=[(1+tanx)(sinx-cosx)+(1-tanx)(sinx+cosx)]/根号2
=[(sinx+tanxsinx-cosx-sinx)+(sinx+cosx-tanxsinx-sinx)]/根号2
=0,
所以向量AB垂直于向量AC;
(2)因为向量BC=向量AC-向量AB
=(sin(x-45)-(1+tanx),sin(x+45)-(1-tanx)),
所以|向量BC|^2
=[sin(x-45)-(1+tanx)]^2+[sin(x+45)-(1-tanx)]^2
=[sin(x-45)^2]^2+(1+tanx)^2+[sin(x+45)]^2+(1-tanx)^2
-2[sin(x-45)(1+tanx)+sin(x+45)(1-tanx)],
由(1)可得,sin(x-45)(1+tanx)+sin(x+45)(1-tanx)=0,
而[sin(x+45)^2]+[sin(x-45)]^2
=(sinx+cosx)^2/2+(sinx-cosx)^2/2
=(sinx)^2+(cosx)^2
=1,
而(1+tanx)^2+(1-tanx)^2
=2(tanx)^2+2,
所以|向量BC|^2
=2(tanx)^2+2+1
=2(tanx)^2+3,
因为x属于[-45度,45度],
所以tanx属于[-1,1],
所以(tanx)^2属于[0,1],
所以|向量BC|^2属于[3,5],
所以|向量BC|属于[根号3,根号5].
所以|向量BC|的取值范围为[根号3,根号5].