Question 1153915
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<pre>

(1)  First, you should not use half-angle formulas.



(2)  Second, for the given purposes, special formulas do exist in Trigonometry, that are called the double argument formulas.


     These formulas are


         {{{cos(2alpha) = 2*cos^2(alpha) - 1}}}

         {{{sin(2alpha) = 2*sin(alpha)*cos(alpha)}}}

         {{{tan(2alpha)}}} = {{{(2*tan(alpha))/(1-tan^2(alpha))}}}.



(3)  So, start calculating

         {{{cos(alpha)}}} = +/- {{{sqrt(1-sin^2(alpha))}}} = +/- {{{sqrt(1-(-3/5)^2)}}} = +/- {{{sqrt(1-9/25)}}} = +/- {{{sqrt(16/25)}}} = +/- {{{4/5}}}.


      Which sign to chose there, is the unknown fact - the problem does not provide a necessary info for it.


      In this sense, your input is FATALLY incomplete.



(4)  Having values of  {{{sin(alpha)}}}  and {{{cos(alpha)}}}, you should substitute them into formulas for double arguments above,

     and complete the assignment in this way.
</pre>

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Again, the input is FATALLY INCOMPLETE; therefore, I can not continue.


The fact that the input is incomplete, is <U>your FAULT</U>.


and my conclusion is that the problem is presented in the post EXTREMELY UNPROFESSIONALLY.