,求下列各式的值.(1)
;
(2)sin2θ-3sinθ·cosθ-1;
(3)
sin2θ+
cos2θ.
,求下列各式的值.(1);
(2)sin2θ-3sinθ·cosθ-1;
(3)sin2θ+cos2θ.
解析:(1)原式=
==.
(2)原式=cos2θ(-
)-1
=cos2θ(tan2θ-3tanθ)-1
=
(tan2θ-3tanθ)-1
=
×(
+
)-1=
-1=
.
(3)原式=
=
=
=
.