In a triangle with a square corner (a right angle), each of the other two corners has a cosine. You find it by taking the side that sits next to that corner — not the long side — and dividing it by the long side (the side across from the square corner). The number you get is the cosine of that angle.

In a triangle with a square corner (a right angle)在一個有直角(square corner)的三角形裡, each of the other two corners另外兩個角 has a cosine各自都有一個cosine(餘弦)。 You find it你要找出它 by taking the side that sits next to that corner的方法是拿緊鄰那個角的邊 — not the long side不是最長的那邊 — and dividing it by the long side再除以最長的邊 (the side across from the square corner)(也就是直角對面的邊)。 The number you get你得到的這個數字 is the cosine of that angle就是那個角的cosine。

Though actually, cosine is not the size of the angle in degrees. It is a ratio: one length divided by another. People still say “the cosine of the angle,” meaning that number.

Though actually不過其實, cosine is not the size of the angle in degreescosine不是角度的大小。 It is a ratio它是一個比值: one length divided by another一個長度除以另一個長度。 People still say “the cosine of the angle,”人們還是會說「the cosine of the angle」, meaning that number意思就是指那個數字。

It is a school and science word; nobody asks for the cosine of something in a shop. Students always meet it in a set with sine and tangent.

It is a school and science word這是學校和科學用語; nobody asks for the cosine of something in a shop沒有人會在店裡問什麼東西的cosine。 Students always meet it學生總是會遇到它 in a set with sine and tangent跟sine(正弦)和tangent(正切)一起出現。

The name is a clue: cosine was short for Latin “sine of the complement.” The complement is the other acute angle that sits with it to make 90 degrees, and the cosine of one angle is the sine of that other one. In maths, people often write cos as a short form.

The name is a clue這個名字本身就是線索: cosine was short for Latin “sine of the complement.”cosine是拉丁文「sine of the complement」(餘角的正弦)的縮寫 The complement is the other acute angle that sits with it to make 90 degreescomplement(餘角)是跟它加起來等於90度的另一個銳角, and the cosine of one angle is the sine of that other one而一個角的cosine就是另一個角的sine。 In maths在數學裡, people often write cos人們常常寫成cos as a short form當作簡寫。