# Derivative of vector valued function

The following is given for $∂x^TAx/∂x$ in a book on Matrix Algebra:

What I cannot understand is: Where does $A^T$ come from in the second row (in the term $ty^TA^Tx$)?

Since $a=a^T$ for a scalar value $a$, $$tx^TAy=t(x^TAy)^T=ty^TA^Tx$$