<PRE><B>Question 1190008</B>
.


Use the basic &amp;nbsp;Trigonometry formula  &amp;nbsp;&amp;nbsp;cos(2A) = 2*cos^2(A) - 1.


Substitute &amp;nbsp;cos(A) = 2/5 &amp;nbsp;here &amp;nbsp;(as it is given), &amp;nbsp;and complete the calculation on your own.


---------------


See the compendium of basic Trigonometry formulas in the lesson

&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;- &lt;A HREF=https://www.algebra.com/algebra/homework/Trigonometry-basics/Compendium-of-Trigonometry-Formulas.lesson&gt;FORMULAS FOR TRIGONOMETRIC FUNCTIONS&lt;/A&gt;

in this site.


In the future, &amp;nbsp;consult this lesson every time as you need some basic Trigonometry formula.



</PRE>