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Paballo Peblo
Paballo Peblo asked in Science & MathematicsMathematics · 8 years ago

given:sin2x=(√15)/8 determine cosx?

given:sin2x=(√15)/8 determine cosx. plz explain the procedure aswell

Update:

btw x E [45;90]

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  • Aleko
    Lv 6
    8 years ago

    from the basic trig equation sin(2x)= sqrt(1-cos^2(2x))

    so sqrt(1-cos^2(2x)=sqrt(15)/8 square both sides to get :

    1-cos^2(2x)=15/64 cos^2(2x)= 49/64 and cos^2(2x)=7/8

    but cos^2(2x)=cos^2x-sin^2x so 2cos^2x=7/8+1

    cos^2x=15/16 and cosx=sqrt(15)/4

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