Cham
Lv 5
Cham asked in 科學及數學數學 · 1 decade ago

Maths MC

Please complete the following MC with explanations.

1 Answer

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  • NCY
    Lv 7
    1 decade ago
    Favorite Answer

    The answer is C

    BD = √(a2 + a2)

    BD = (√2)a

    BF = BD = (√2)a

    ∠BCE = 45˚

    By the sin law,

    BC / sin∠BFC = BF / sin45˚

    a / sin∠BFC = (√2)a / (1/√2)

    1/2 = sin∠BFC

    ∠BFC = 30˚

    ∠BDE = ∠BFC = 30˚

    length of the perpendicular from B to DE

    = (√2)a×sin30˚

    = (√2)a / 2

    = a / √2

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