Calculate the sum of areas of the three squares
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Solution
We have a top part of a circle of diameter \(5\) drawn with three squares. To start let \(a\) be the side length of the blue square, and \(b\) the side length of the green square
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As we see in the previous figure the side of the grey square equals to \(a+b\). Let’s take the next example of similar right triangles
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We get these results: \[a^{2}=d^{2}+h^{2}\] \[b^{2}=e^{2}+h^{2}\] \[\left(d+e\right)^{2}=a^{2}+b^{2}\] \[d^{2}+e^{2}+2de=a^{2}+b^{2}\] \[d^{2}+e^{2}+2de=d^{2}+h^{2}+e^{2}+h^{2}\] \[2de=2h^{2}\] \[h^{2}=de\]
Now let’s return to our problem and apply the previous result to the next figure
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Therefore we get, \[b^{2}=\left(b-a\right)\left(2a+b\right)\] \[=2ab+b^{2}-2a^{2}-ab\] \[2a^{2}-ab=0\] \[a\left(2a-b\right)=0\] \[\color{blue} {a\neq0}\] \[\Rightarrow2a=b\] Using another fact in the figure, we have \[\left(b-a\right)+a+\left(a+b\right)=5\] \[2b+a=5\] \[2\left(2a\right)+a=5\] \[5a=5\] \[a=1\] Finally, let \(S\) be the sum of areas of the three squares, thus \[S=a^{2}+b^{2}+\left(a+b\right)^{2}\] \[=a^{2}+b^{2}+a^{2}+b^{2}+2ab\] \[=2a^{2}+2b^{2}+2ab\] \[=2\left(a^{2}+b^{2}+ab\right)\] \[=2\left(a^{2}+4a^{2}+2a^{2}\right)\] \[=14a^{2}\] \[\large \Rightarrow S=14\]
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