Question 1114003
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<pre>
{{{13^2 }}} = {{{7^2 + x^2 - 2*7*x*cos(60^o)}}} 


169 = 49 + {{{x^2 -7x}}},


{{{x^2 - 7x - 120}}} = 0


(x-15)*(x+8) = 0


We are looking for the positive root, therefore, the only solution is x= 15.
</pre>

<U>Answer</U>.  &nbsp;&nbsp;x = 15.