先把前两个当成整体，然后按乘法的求导法则做两次就可以了
=[F(x)]'*[G(x)*T(x)]+[F(x)]*[G(x)*T(x)]'=[F(x)]'*[G(x)*T(x)]+[F(x)]*{[G(x)]'*T(x)]+[G(x)]*[T(x)]'}=[F(x)]'*G(x)*T(x)+F(x)*[G(x)]'*T(x)+F(x)*G(x)*T(x)]'
