Question 1170274
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                Watch attentively each my step (!)



<pre>
tan(a) = {{{h/40}}}


tan(b) = {{{h/120}}}


a + b = {{{pi/2}}}  ====>  a = {{{pi/2}}} - b


tan(a) = {{{tan(pi/2-b)}}} = {{{1/tan(b)}}}  ====>


{{{h/40}}} = {{{1/((h/120))}}} = {{{120/h}}}  ====>


{{{h^2}}} = 40*120 = 40*40*3


h = {{{sqrt(40*40*3)}}} = {{{40*sqrt(3)}}} = 69.282 meters.    <U>ANSWER</U>
</pre>

Solved and explained in all details.