已知△ABC中,cotA=-125,则cosA=( ) A.1213 B.513 C.−513 D.−1213
已知△ABC中,cotA=-
,则cosA=( )
A.
B.
C.
−D.
−
数学人气:324 ℃时间:2020-02-02 16:40:13
优质解答
∵cotA=
−∴A为钝角,cosA<0排除A和B,
再由cotA=
=
−,和sin
2A+cos
2A=1求得cosA=
−,
故选D.
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