求值:|2+2e25πi+e65πi|.-数学

题目简介

求值:|2+2e25πi+e65πi|.-数学

题目详情

求值:|2+2e
2
5
πi
+e
6
5
πi
|
题型:解答题难度:中档来源:不详

答案

原式=|2+2(cosclass="stub"2π
5
+isinclass="stub"2π
5
)+cosclass="stub"6π
5
+isinclass="stub"6π
5
|
=
(2+2cosclass="stub"2π
5
+cosclass="stub"6π
5
) 2+(2sinclass="stub"2π
5
+sinclass="stub"6π
5
) 2

=
4+4(cos2class="stub"2π
5
+sin2class="stub"2π
5
)+(cos2class="stub"6π
5
+sin2class="stub"6π
5
) +4(cosclass="stub"2π
5
cosclass="stub"6π
5
+sinclass="stub"2π
5
sinclass="stub"6π
5
)+8cosclass="stub"2π
5
+4cosclass="stub"6π
5
       

=
9+4cosclass="stub"4π
5
+ 8cosclass="stub"2π
5
-4cosclass="stub"π
5

=
9+ 8cosclass="stub"2π
5
-8cosclass="stub"π
5

cosclass="stub"2π
5
-cosclass="stub"π
5
=
sinclass="stub"π
5
(cosclass="stub"2π
5
-cosclass="stub"π
5
sinclass="stub"π
5
=
sinclass="stub"3π
5
-sinclass="stub"π
5
-sinclass="stub"2π
5
2sinclass="stub"π
5
=-class="stub"1
2

9+ 8cosclass="stub"2π
5
-8cosclass="stub"π
5
=
9+8×(-class="stub"1
2
=
5

所以,|2+2eclass="stub"2
5
πi
+eclass="stub"6
5
πi
|
=
5

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