设f（x）=x-sinxcosxcos2xg（x）=ln(1+sin4x)x，x≠00x＝0，则当x→0時f（x）是g（x）的（　　）A．高阶无穷小B．低阶无穷小C．同阶非等价无穷小D．等价无穷小... 设f（x）=x-sinxcosxcos2x，g（x）=ln(1+sin4x)xx≠00，x＝0则当x→0时，f（x）是g（x）嘚（　　）A．高阶无穷小B．低阶无穷小C．同阶非等价无穷小D．等价无穷小