余弦 is read as よげん (yogen) and means cosine.
よげん
yogen
ほうこうよげん
direction cosine
よゆう
composure
よか
leisure
よぎない
unavoidable
よぎなく
unavoidably
よじょう
surplus
よいん
suggestiveness (of a book, poem, etc.)
よきょう
performance (at a party or banquet, etc.)
よめいせんこく
telling a patient how long they have left to live
よたく
blessings
よじょうじんいん
excess personnel
よゆうしゅ
free move (othello)