10th Class Mathematics Introduction to Trigonometry Question Bank Trigonometry

  • question_answer
    If\[sin\text{ }A+cosec\,\,A=2\], then what is the value of the value of \[\frac{{{\sin }^{4}}A+1}{{{\sin }^{2}}A}\]?

    A)  0                    

    B)  1            

    C)  2      

    D)  \[6/\sqrt{2}\]

    Correct Answer: C

    Solution :

    (c):        \[\sin A+\frac{1}{\operatorname{sinA}}=2\] \[\Rightarrow \]   \[{{\sin }^{2}}A+1=2\sin A\] \[\Rightarrow \]   \[{{\sin }^{2}}A-2\sin A+1=0\] \[\Rightarrow \]   \[{{(sinA-1)}^{2}}=0\] \[\Rightarrow \]   \[\sin A=1\] \[\therefore \]      \[\frac{{{\sin }^{4}}A+1}{{{\sin }^{2}}A}=\frac{1+1}{1}=2\] Again here, you can straightaway conclude that \[\sin A=1\] \[\therefore \]      \[\frac{{{\sin }^{4}}A+1}{{{\sin }^{2}}A}=\frac{1+1}{1}=2\]                      


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