唔識做功課56

1.
cos a = -cos45°
cos a = -√2 / 2　[Then, we know that a is in QII or QIII]
a = 180° - 45° or a = 180° + 45°
a = 135° or a = 225°

2.
tan a = -cos17°
tan a = -0.956304756　[Then, we know that a is in QII or QV]
[Use calculator to consider what value of b would give tan b = 0.956304756.]
[It turns out that b = 43.72047703°.]
Therefore,
a = 180° - 43.72047703° or a = 360° - 43.72047703°
a = 136.27952297° or a = 316.27952297°


2015-03-21 17:42:48 補充：
In Q2, [Then, we know that a is in QII or QIV]

2015-03-22 23:17:01 補充：
為了令同學容易去明白和計算，使用以下的步驟：

（１）先判斷是哪一個象限 (quadrant)：１，２，３，４

（２）不理正負，全部當正數計出角度（那麼這角度必定是小於 90°，稱為 a）

（３）最後，根據（１）在以下四項中選適當的作答： a, 180° - a, 180° + a, 360° - a。

2015-03-22 23:18:26 補充：
例如：cos(x) = -0.6

（１）首先知道 x 是在 QII 或 QIII

（２）然後想像 cos(a) = 0.6 得 a = 53.13°

（３）答案是 x = 180° - 53.13° 或 x = 180° + 53.13°

2015-03-23 19:45:02 補充：
客氣啦~
你咁勤力, 希望你可以考得好成績。

[Use calculator to consider what value of b would give tan b = 0.956304756.]
[It turns out that b = 43.72047703°.]唔明点解要求出tan b,亦唔明白負0.9563...為何變成正0.9563...唔好意思呀,哩課有好多唔明白嘅地方,請知識長再指点一下！

2015-03-23 18:44:22 補充：
其實miss冇教我當正數計出角度,所以我冇辦法計得到,我再將exercise重做咗一次,全對喇!所以...知識長好多謝你!