问题
解答题
已知cos(α+
|
答案
cos(2α+
π |
4 |
π |
4 |
π |
4 |
| ||
2 |
3π |
4 |
7π |
4 |
π |
4 |
3π |
4 |
π |
4 |
7π |
4 |
∴sin(α+
π |
4 |
1-cos2(α+
|
4 |
5 |
从而cos2α=sin(2α+
π |
2 |
π |
4 |
π |
4 |
24 |
25 |
sin2α=-cos(2α+
π |
2 |
π |
4 |
7 |
25 |
∴cos(2α+
π |
4 |
| ||
2 |
24 |
25 |
7 |
25 |
31
| ||
50 |
已知cos(α+
|
cos(2α+
π |
4 |
π |
4 |
π |
4 |
| ||
2 |
3π |
4 |
7π |
4 |
π |
4 |
3π |
4 |
π |
4 |
7π |
4 |
∴sin(α+
π |
4 |
1-cos2(α+
|
4 |
5 |
从而cos2α=sin(2α+
π |
2 |
π |
4 |
π |
4 |
24 |
25 |
sin2α=-cos(2α+
π |
2 |
π |
4 |
7 |
25 |
∴cos(2α+
π |
4 |
| ||
2 |
24 |
25 |
7 |
25 |
31
| ||
50 |