Question 1174443
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Hi

<img src=" http://upload.wikimedia.org/wikipedia/commons/thumb/7/7e/Trigonometry_triangle.svg/200px-Trigonometry_triangle.svg.png ">

According to the diagram:
 h = 90cm
 a = 72cm
 b = height of cinder block
Pythagorean theorem:  a^2 + b^2 = h^2
  72^2 + b^2 = 90^2
use Your Calculator: b^2 = 90^2 - 72^2 = 2916
    b = √2916 = 54cm       (tossing out negative solution for length)


Wish You the Best in your Studies.
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