解题思路：由
sin(
π
4
+x)＝
12
13
(
π
4
＜x＜
π
2
)
得，cos
(
π
4
+x)
=-[5/13]，从而cos2x=sin
(
π
2
+2x)
=2sin
(
π
4
+x)
cos
(
π
4
+x)
=-[120/169]，cos
(
π
4
−x)
=cos
[
π
2
−(
π
4
+x)]
=sin
(
π
4
+x)
=[12/13]．然后可得出式子[cos2x
已知sin(π4+x)＝1213(π4＜x＜π2)，则式子[cos2xcos(π/4−x)]的值为（ ）
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