Brian asked in 科學及數學數學 · 1 decade ago

cos sin tan 既野...數學勁既請入

今日..老師寫左d notes ...↓



係唔係有步驟跟..? 第一步應該點做....


1 Answer

  • 1 decade ago
    Favorite Answer

    example like first question,

    start for the complicated part, which is the left hand side,

    (sec x - cos x)/sec x

    = ( (1/cos x) - cos x ) / (1/cos x)

    = ( (1-cos^2) / cos x) / (1/cos x)

    by definition, 1-cos^2 x = sin^2 x

    = (sin^2 x/ cos x) / (1/cos x)

    = sin^2 x

    question 2,

    tan x + cot x = sinx cos x

    at the left hand side,

    sin x / cos x + cos x / sin x

    = sin^2/ sin x cos x + cos^2 / sinx cos x

    = 1 / sinx cos x

    then second question is not identity

    basically, u need to transform all tan, cot, csc, and sec become sin and cos. that makes life better.. =)

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