Question 1107872
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First step is &nbsp;<U>TO LEARN</U>&nbsp; sum and difference identities.


See the lessons

&nbsp;&nbsp;&nbsp;&nbsp;- <A HREF=https://www.algebra.com/algebra/homework/Trigonometry-basics/Compendium-of-Trigonometry-Formulas.lesson>FORMULAS FOR TRIGONOMETRIC FUNCTIONS</A>

&nbsp;&nbsp;&nbsp;&nbsp;- <A HREF = http://www.algebra.com/algebra/homework/Trigonometry-basics/Addition-and-subtraction-formulas.lesson>Addition and subtraction formulas</A>

&nbsp;&nbsp;&nbsp;&nbsp;- <A HREF = http://www.algebra.com/algebra/homework/Trigonometry-basics/Addition-and-subtraction-formulas-Examples.lesson>Addition and subtraction formulas - Examples</A>


in this site.


Second step is to learn on how to apply them.


    a)  {{{cos(2x-pi/2)}}} = {{{cos(2x)*cos(pi/2) + sin(2x)*sin(pi/2)}}} = cos(2x)*0 + sin(2x)*1 = sin(2x);


    b)  sin(2x) = sin(x+x) = sin(x)*cos(x) + cos(x)*sin(x) = 2*sin(x)*cos(x).


<U>Answer</U>.  {{{cos(2x-pi/2)}}} = 2*sin(x)*cos(x).
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That's all.