Answer:
Step-by-step explanation:
cos (x-y)=cos x cos y+sin x sin y
cos(45-β)=cos~45~cos~β+sin~45~sin~β
[tex]cos~45=sin~45=\frac{1}{\sqrt{2} }\\cos (45-\beta )=\frac{1}{\sqrt{2} } ~cos~\beta +\frac{1}{\sqrt{2} } ~sin~\beta \\=\frac{1}{\sqrt{2} } (cos~\beta +sin~\beta )[/tex]
