涓皬瀛︽暀鑲叉暀瀛﹁祫鏂?/p>
涓撻鑳藉姏鎻愬崌缁冧竷涓夎鎭掔瓑鍙樻崲涓庤В涓夎褰?/p>
(45
鍒嗛挓
80
鍒?/p>
)
涓�銆侀�夋嫨棰?/p>
(
姣忓皬棰?/p>
5
鍒?/p>
,
鍏?/p>
30
鍒?/p>
)
1.
cos15掳
-4sin
2
15掳cos15掳=()
A.
B.
C.1D.
銆愯В鏋愩�?/p>
閫?/p>
D.
cos 15
掳
-4sin
2
15
掳
cos 15
掳
=
cos 15
掳
-2sin 15
掳脳
2sin 15
掳
cos 15
掳
=
cos 15
掳
-2sin 15
掳
sin 30
掳
=
cos 15
掳
-sin 15
掳
=2cos(15
掳
+30
掳
)=
.
2.(2018
路姘稿窞浜屾ā
)
宸茬煡鈻?/p>
ABC
鐨勫唴瑙?/p>
A,B,C
鐨勫杈瑰垎鍒槸
a,b,c,
鑻?/p>
+
=2a,
鍒欌柍
ABC
鏄?/p>
()
A.
绛夎竟涓夎褰?/p>
B.
閿愯涓夎褰?/p>
C.
绛夎叞鐩磋涓夎褰?/p>
D.
閽濊涓夎褰?/p>
銆?/p>
瑙?/p>
鏋?/p>
銆?/p>
閫?/p>
C.
鍥?/p>
涓?/p>
+
=2a,
鎵�
浠?/p>
鐢?/p>
姝?/p>
寮?/p>
瀹?/p>
鐞?/p>
鍙?/p>
寰?/p>
,
+
=2sinA
鈮?
2
=2,
鎵�浠?/p>
sin A=1,
褰?/p>
=
鏃?/p>
,
鈥?/p>
=
鈥濇垚绔?/p>
,
鎵�浠?/p>
A=
,b=c,
鎵�浠モ柍
ABC
鏄瓑鑵扮洿瑙掍笁瑙掑舰
.
3.(2018
路鍏ㄥ浗鍗封叀
)
鍦ㄢ柍
ABC
涓?/p>
,cos
=
,BC=1,AC=5,
鍒?/p>
AB=()
A.4
B.
C.
D.2