Question 1162367
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<pre>

Use the basic <U>argument addition formula</U> for cosine 


    cos(a+b) = cos(a)*cos(b) - sin(a)*sin(b) 


and you momentarily get


    cos(4x)*cos(3x) - sin(4x)*sin(3x) = cos(4x + 3x) = cos(7x).    <U>ANSWER</U>
</pre>

Solved.