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Mathematics
Mathematics
Problem
If
cos
x
+
sin
x
=
a
(
−
π
2
<
x
<
−
π
4
)
\cos x + \sin x = a\left(-\frac{\pi}{2} < x < -\frac{\pi}{4}\right)
cos
x
+
sin
x
=
a
(
−
2
π
<
x
<
−
4
π
)
, then
cos
2
x
\cos 2x
cos
2
x
is equal to a.
a
2
a^2
a
2
b.
a
(
2
−
a
)
a\sqrt{(2-a)}
a
(
2
−
a
)
c.
a
(
2
+
a
)
a\sqrt{(2+a)}
a
(
2
+
a
)
d.
a
(
2
−
a
2
)
a\sqrt{(2-a^2)}
a
(
2
−
a
2
)
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