Question

求解划线部分，是高一数学的一道题

Answer 1

cos(105º-α)
=cos(180º-75º-α)
=cos[180º-(75º+α)]
=-cos(75º+α)=-1/3
sin(α-105º)
=sin[α-(180º-75º)]
=sin(α-180º+75º)
=sin[-(180º-α-75º)]
=-sin[180º-(75º+α)]
=-sin(75º+α)

Answer 2

B代表β，A代表α，数字中的度数符号°未写
cos(B)=-cos(180-B)
B=105-A
cos(105-A)=-cos(180-105+A)=-cos(75+A)
sin(B)=sin(180-B)
sin(105-A)=-sin(A-105)=sin(180-105+A)=sin(75+A)