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Question

Value of sin4π8+sin43π8+sin45π8+sin47π8 is equal to:

A
1
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B
2
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C
3/2
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D
1/2
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Solution

The correct option is D 3/2
sin4π8+sin43π4+sin45π8+sin47pi8
=(sin2π8)2+(sin23π8)2+(sin25π8)2+(sin27π8)2
=⎜ ⎜1cosπ42⎟ ⎟2+⎜ ⎜ ⎜1cos3π42⎟ ⎟ ⎟2+⎜ ⎜ ⎜1cos5π42⎟ ⎟ ⎟2+⎜ ⎜ ⎜1cos7π42⎟ ⎟ ⎟2
=⎜ ⎜ ⎜ ⎜1222⎟ ⎟ ⎟ ⎟2+⎜ ⎜ ⎜ ⎜1+222⎟ ⎟ ⎟ ⎟2+⎜ ⎜ ⎜ ⎜1+222⎟ ⎟ ⎟ ⎟2+⎜ ⎜ ⎜ ⎜1222⎟ ⎟ ⎟ ⎟2
=2(224)2+2(2+24)2
=18(22)2+18(2+2)2
=18(442+2+4+42+2)
=128
=32

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