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Given that SIN Theta = -1/sqrt(10) and theta is in quadrant 4, find sin2theta and cos2theta.

I'm not sure how to properly square the -1/sqrt10 and keep an exact answer other than decimal. Otherwise, my final answer is 1.632455533

  • Pre-Calculus -

    if sintheta=-1/sqrt10, then
    costheta= (10-1)/sqrt10= sqrt (9/10)
    check those.

    Then sin2theta= sintheta*costheta=-2/sqrt10*sqrt9/10
    = sqrt9 /5=3/5=.6

    cos2Theta=1-2sin^2 theta=1-2(1/10)=.8

    check all that. I have no idea what you did.

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