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Introduction to Trigonometry Test - 21

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Introduction to Trigonometry Test - 21
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  • Question 1
    1 / -0
    If $$\sec{2A}=\csc{(A-42^\circ)}$$ where $$2A$$ is acute angle then value of $$A$$ is
    Solution
    $$\sec{2A}=\csc{(A-42^\circ)}$$
    $$\csc{(90-2A)}=\csc{(A-42^\circ)}$$
    $$90-2A=A-42$$
    $$3A=132$$
    $$A=44^\circ$$
  • Question 2
    1 / -0
    The value of $$\displaystyle\frac{\cot{40^\circ}}{\tan{50^\circ}}-\frac{1}{2}\left(\frac{\cos{35^\circ}}{\sin{55^\circ}}\right)$$ is ____________.
    Solution
    $$\displaystyle\frac{\cot{40^\circ}}{\tan{50^\circ}}-\frac{1}{2}\left(\frac{\cos{35^\circ}}{\sin{55^\circ}}\right)$$

    $$=\displaystyle\frac{\cot{(90^\circ-50^\circ)}}{\tan{50^\circ}}-\frac{1}{2}\left(\frac{\cos{(90^\circ-55^\circ)}}{\sin{55^\circ}}\right)$$

    $$=\displaystyle\frac{\tan{50^\circ}}{\tan{50^\circ}}-\frac{1}{2}\left(\frac{\sin{55^\circ}}{\sin{55^\circ}}\right)$$

    $$=1-\dfrac 1 2$$

    $$=\dfrac 1 2$$
  • Question 3
    1 / -0
    If $$\displaystyle  2\sin 2\theta =\sqrt{3}$$ then the value of $$\displaystyle  \theta$$ is
    Solution
    $$2sin  2\theta=\sqrt{3}$$
    $$\Rightarrow sin  2\theta=\dfrac{\sqrt{3}}{2}$$
    $$\because sin60^\circ{}=\dfrac{\sqrt{3}}{2}$$
    $$\therefore sin  2\theta=sin 60^\circ{}$$
    $$\Rightarrow 2\theta=60^\circ{}$$
    $$\Rightarrow \theta=\dfrac{60}{2}=30^\circ{}$$


  • Question 4
    1 / -0
    For an acute angle $$\theta$$ in a right angled triangle, $$\dfrac{1}{\text{cosec}\,{\theta}} =$$
    Solution

    $$\sin \theta=\dfrac{opposite}{hypotenuse}$$ 

    $$\cos \theta = \dfrac{adjacent}{hypotenuse}$$ 

    $$\text{cosec}\ \theta = \dfrac{hypotenuse}{opposite}$$
    $$\dfrac{1}{\text{cosec}\ \theta}=\dfrac{1}{\dfrac{hypotenuse}{opposite}}=\dfrac{opposite}{hypotenuse}=\sin\ \theta$$
    $$\therefore\ \dfrac{1}{\text{cosec}\ \theta}=\sin\ \theta$$

  • Question 5
    1 / -0
    The value of $$\cos0^0$$ is ______.
    Solution
    Using the trigonometric table
    The value of $$\cos { 0^\circ  } $$  is 1
  • Question 6
    1 / -0
    $${\sec}^{2}{60^o} - 1= $$
    Solution
    To find:
    $$\sec ^{ 2 }{  { 60^o-1 }  } $$
     $$={ \left( 2 \right)  }^{ 2 }-1$$
     $$=4-1=3$$
  • Question 7
    1 / -0
    The value of $$\left(\cos{60^o} \cos{30^o} - \sin{60^o} \sin{30^o}\right)$$ is
    Solution
    Given that: $$\left( \cos { 60^o } \cos { 30^o-\sin { 60^o } \sin { 30^o }  }  \right) $$
     $$=\dfrac { 1 }{ 2 } \times \dfrac { \sqrt { 3 }  }{ 2 } -\dfrac { \sqrt { 3 }  }{ 2 } \times \dfrac { 1 }{ 2 } $$
     $$=\dfrac { \sqrt { 3 }  }{ 4 } -\dfrac { \sqrt { 3 }  }{ 4 } $$
     $$=0$$
  • Question 8
    1 / -0
    For an acute angle $$\theta$$ in a right angled triangle, $$\dfrac{\sin{\theta}}{\cos{\theta}} =$$
    Solution

    $$\sin \theta=\dfrac{opposite}{hypotenuse}$$ 

    $$\cos \theta = \dfrac{adjacent}{hypotenuse}$$ 

    $$\dfrac{\sin \theta}{\cos \theta}=\dfrac{\frac{opposite}{hypotenuse}}{\frac{adjacent}{hypotenuse}}$$
            
                $$=\dfrac{opposite}{adjacent}\times \dfrac{hypotenuse}{hypotenuse}$$

                $$=\dfrac{opposite}{adjacent}$$
                $$=\tan \theta$$
    Hence, $$\dfrac{\sin \theta}{\cos \theta}=\tan \theta$$.

  • Question 9
    1 / -0
    For an acute angle $$\theta$$ in a right angled triangle, $$\dfrac{\cos{\theta}}{\sin{\theta}} =$$
    Solution
    $$\mathrm \sin \theta=\dfrac{\mathrm opposite}{\mathrm hypotenuse}$$ 

    $$\cos \theta = \dfrac{\mathrm adjacent}{\mathrm hypotenuse}$$ 

    $$\dfrac{\cos \theta}{\sin \theta}=\dfrac{\frac{\mathrm adjacent}{\mathrm hypotenuse}}{\frac{\mathrm opposite}{\mathrm hypotenuse}}$$
            
                $$=\dfrac{adjacent}{opposite}\times \dfrac{hypotenuse}{hypotenuse}$$

                $$=\dfrac{adjacent}{opposite}$$
                $$=\cot \theta$$
    Hence, $$\dfrac{\cos \theta}{\sin \theta}=\cot \theta$$.

  • Question 10
    1 / -0
    For an acute angle $$\theta$$ in a right angled triangle, $$\dfrac{1}{\tan{\theta}} =$$
    Solution

    $$\sin \theta=\dfrac{opposite}{hypotenuse}$$ 

    $$\cos \theta = \dfrac{adjacent}{hypotenuse}$$ 

    $$\dfrac{\sin \theta}{\cos \theta}=\dfrac{\frac{opposite}{hypotenuse}}{\frac{adjacent}{hypotenuse}}$$
                $$=\dfrac{opposite}{adjacent}$$
                $$=\tan \theta$$
    $$\therefore \dfrac{\sin \theta}{\cos \theta}=\tan \theta$$.

    $$\dfrac{1}{\tan \theta}=\dfrac{\cos \theta}{\sin \theta}=\dfrac{\frac{adjacent}{hypotenuse}}{\frac{opposite}{hypotenuse}}$$
                 $$=\dfrac{adjacent}{opposite}$$
                 $$=\cot \theta$$
    $$\therefore \dfrac{1}{\tan \theta}=\cot \theta$$

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