Question 1153127
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The formulation in the post is 100% wrong.   An hieroglyph like   " sin(-4/7) "    is  NEVER  USED  in  Math.


It is not possible to answer correctly in this formulation.


I agree with tutor @greenestamps.


The correct formulation (and uniquely possible in this context) is 


<pre>
    Find exact value of  {{{cos(arcsin(-4/7))}}}.
</pre>

The answer then is  


<pre>
    {{{cos(arcsin(-4/7))}}} = {{{sqrt(1- (-4/7)^2)}}} = {{{sqrt(1 - 16/49)}}} = {{{sqrt(33)/7}}}.
</pre>


It seems to me sometimes, that there is a special person on the opposite end of the Internet, who intently corrupts every coming post.