tan10°+tan50°+tan120°tan10°•tan50°的值应是( ) A.-1 B.1 C.-3 D.3
问题描述:
的值应是( )tan10°+tan50°+tan120° tan10°•tan50°
A. -1
B. 1
C. -
3
D.
3
答
=tan10°+tan50°+tan120° tan10°•tan50°
+tan10°+tan50° tan10°•tan50°
tan120° tan10°•tan50°
=
-tan60°(1−tan10°tan50°) tan10°•tan50°
tan60° tan10°•tan50°
=
-
3
tan10°tan50°
-
3
=-
3
tan10°tan50°
,
3
故选C.