Question 1161443
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Assuming the tree is on level ground, the tree, its shadow, and the line from the top of the tree to the tip of the shadow form a right triangle.  So use the Pythagorean Theorem with the given expressions.<br>
{{{(x+3)^2 = x^2+(x-21)^2}}}<br>
{{{x^2+6x+9 = x^2+x^2-42x+441}}}<br>
{{{0 = x^2-48x+432}}}<br>
{{{0 = (x-36)(x-12)}}}<br>
{{{x = 36}}} or {{{x = 12}}}<br>
With x-21 as the length of the shadow, x=12 makes no sense.  So<br>
ANSWER:
height of tree = x = 36m
length of shadow = x-21 = 15m
distance from top of tree to tip of shadow = x+3 = 39m<br>