The answer is true
Using A x = b {\displaystyle \displaystyle Ax=b} we see that
y T b = y T A x = ( A y T ) T x = 0 {\displaystyle \displaystyle y^{T}b=y^{T}Ax=(Ay^{T})^{T}x=0}
valid since A y T = 0 {\displaystyle \displaystyle Ay^{T}=0}
