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    Question

    The value of cosĀ² 10Ā° + cosĀ² 20Ā° + cosĀ² 30Ā° +

    ā€¦ā€¦. + cosĀ² 90Ā° is
    A 4 Correct Answer Incorrect Answer
    C -1 Correct Answer Incorrect Answer
    D 1 Correct Answer Incorrect Answer

    Solution

    ATQ, We know cos(90Ā° - A) = sin A cosĀ² 10 + cosĀ² 20 + cosĀ² 30Ā° +ā€¦ā€¦. + cosĀ² 90Ā° = cosĀ² 1 + cosĀ² 20 + cosĀ² 30Ā° + cosĀ² 40Ā° + sinĀ² 40+ sinĀ² 30Ā° + sinĀ² 20 + sinĀ² 10+ cosĀ² 90 = (sınĀ² 10Ā° + cos2 10) + (sinĀ² 20 + cosĀ² 20) + (sinĀ² 30Ā° + cosĀ² 30) + (sinĀ² 40+ cosĀ² 40Ā°) + cosĀ² 90 = 1+1+1+1+0 = 4

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