sin13°cos343°+sin77°sin17°
=sin13°cos（360°-17°）+sin77°sin17°
=sin13°cos（-17°）+sin77°sin17°
=sin13°cos17°+sin77°sin17°
=sin13°cos17°+COS13°sin17°
=SIN(sin13°+17°)
=sin30度=1/2
sin13°cos343° + sin77°sin17°
= sin13°cos17° + sin17°cos13°
= sin(13°+17°)
= sin30°
= 1/2
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