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 Mar 25, 2015

Best Answer 

 #2
avatar+118703 
+10

Mmm,

 

first  α2   is between  45 and 67.5 degrees.   so that is the first quadrant.   All trig ratios are positive

 

so   α    must be between 90 and 135 degrees so that is the second quadrant.  Only sine and cosec are positive all other ratios will be negative,

 

Now

 

\\cos \left(\frac{\alpha}{2}\right)=\frac{5}{8}\\\\  cos^2 \left(\frac{\alpha}{2}\right)=\frac{25}{64}\\\\  cos^2 \left(\frac{\alpha}{2}\right)+sin^2 \left(\frac{\alpha}{2}\right)=1}\\\\  \frac{25}{64}+sin^2 \left(\frac{\alpha}{2}\right)=1}\\\\  sin^2 \left(\frac{\alpha}{2}\right)=1-\frac{25}{64}\\\\  sin^2 \left(\frac{\alpha}{2}\right)=\frac{39}{64}\\\\  sin \left(\frac{\alpha}{2}\right)=\frac{\sqrt{39}}{8}\\\\\\

 

sin(α)=sin(α2+α2)sin(α)=2sinα2cosα2sin(α)=239858sin(α)=39458sin(α)=53932Cosec(α)=32539Cosec(α)=3239539Cosec(α)=3239195

 

cos(α)=cos(α2+α2)cos(α)=cos2(α2)sin2(α2)cos(α)=25643964cos(α)=1464cos(α)=732sec(α)=327

 

\\tan(\alpha)=sin(\alpha)}\div{cos(\alpha)}\\\\  tan(\alpha)=\frac{5\sqrt{39}}{32}\div\frac{-7}{32}\\\\  tan(\alpha)=\frac{5\sqrt{39}}{32}\times\frac{32}{-7}\\\\  tan(\alpha)=-\frac{5\sqrt{39}}{7}\\\\\\  cot(\alpha)=-\frac{7}{5\sqrt{39}}\\\\  cot(\alpha)=-\frac{7\sqrt{39}}{5*39}\\\\  cot(\alpha)=-\frac{7\sqrt{39}}{195}\\\\

 Mar 26, 2015
 #1
avatar+118703 
+5

Melody Mar 26, 2015
 #2
avatar+118703 
+10
Best Answer

Mmm,

 

first  α2   is between  45 and 67.5 degrees.   so that is the first quadrant.   All trig ratios are positive

 

so   α    must be between 90 and 135 degrees so that is the second quadrant.  Only sine and cosec are positive all other ratios will be negative,

 

Now

 

\\cos \left(\frac{\alpha}{2}\right)=\frac{5}{8}\\\\  cos^2 \left(\frac{\alpha}{2}\right)=\frac{25}{64}\\\\  cos^2 \left(\frac{\alpha}{2}\right)+sin^2 \left(\frac{\alpha}{2}\right)=1}\\\\  \frac{25}{64}+sin^2 \left(\frac{\alpha}{2}\right)=1}\\\\  sin^2 \left(\frac{\alpha}{2}\right)=1-\frac{25}{64}\\\\  sin^2 \left(\frac{\alpha}{2}\right)=\frac{39}{64}\\\\  sin \left(\frac{\alpha}{2}\right)=\frac{\sqrt{39}}{8}\\\\\\

 

sin(α)=sin(α2+α2)sin(α)=2sinα2cosα2sin(α)=239858sin(α)=39458sin(α)=53932Cosec(α)=32539Cosec(α)=3239539Cosec(α)=3239195

 

cos(α)=cos(α2+α2)cos(α)=cos2(α2)sin2(α2)cos(α)=25643964cos(α)=1464cos(α)=732sec(α)=327

 

\\tan(\alpha)=sin(\alpha)}\div{cos(\alpha)}\\\\  tan(\alpha)=\frac{5\sqrt{39}}{32}\div\frac{-7}{32}\\\\  tan(\alpha)=\frac{5\sqrt{39}}{32}\times\frac{32}{-7}\\\\  tan(\alpha)=-\frac{5\sqrt{39}}{7}\\\\\\  cot(\alpha)=-\frac{7}{5\sqrt{39}}\\\\  cot(\alpha)=-\frac{7\sqrt{39}}{5*39}\\\\  cot(\alpha)=-\frac{7\sqrt{39}}{195}\\\\

Melody Mar 26, 2015

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