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Richard
Lv 4
Richard asked in Science & MathematicsMathematics · 1 decade ago

Exact Value cos(5pi/18)sin(pi/9) - cos(pi/9)sin(5pi/18)?

Pls give a detailed answer

3 Answers

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  • ted s
    Lv 7
    1 decade ago
    Favorite Answer

    you should know that sin ( a - b ) = sin a cos b - cos a sin b and sin ( - w ) = - sin w

    { - sin π / 6 }...and you should know the numerical value of this .

  • Gass
    Lv 7
    1 decade ago

    cos 5π / 18 = cos (5 . 180 / 18) = cos 50

    cos π / 9 = cos (180 / 9) = cos 20

    sin 5π / 18 = sin (5 . 180 / 18) = sin 50

    = cos (5π / 18) - cos (π / 9) sin (5π / 18)

    = cos 50 - cos 20 . sin 50

    = 0,64 - 0,94 . 0,77

    = -0,0838

    finish

  • Pi R Squared
    Lv 7
    1 decade ago

    Hi,

    cos(A + B) = cos(A)sin(B) - cos(B)sin(A)

    cos(5π/18 + π/9) = cos(5π/18)sin(π/9) - cos(π/9)sin(5π/18)

    cos(5π/18 + π/9) = cos(7π/18) <==ANSWER

    I hope that helps!! :-)

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