f(x)=xTAx  ⟹  ∂f∂x=(AT+A)xf(x)=x^TAx \implies \frac{\partial f}{\partial x} = (A^T+A)x f(β)=2β′x  ⟹  ∂∂βf(β)=2βf(\beta) = 2\beta' x \implies \frac{\partial}{\partial \beta} f(\beta) = 2 \beta

Cover letter: https://www.themuse.com/advice/cover-letter-examples-every-type-job-seeker?sc_src=email_891957&sc_lid=59217234&sc_uid=SS5WpSeD5X&sc_llid=201685&sc_eh=574eefa43680980c1&utm_source=emarsys&utm_medium=email&utm_campaign=daily_20210203NoSpon_90Day_891957&utm_content=sponsored&utm_term=&uid=887470193