\(B=\sqrt{4-\sqrt{7}}-\sqrt{4+\sqrt{7}}\)
\(\sqrt{2}.B=\sqrt{8+2\sqrt{7}}-\sqrt{8-2\sqrt{7}}\)
\(\sqrt{2}.B=\sqrt{\left(\sqrt{7}+1\right)^2}-\sqrt{\left(\sqrt{7}-1\right)^2}\)
\(\sqrt{2}.B=\left|\sqrt{7}+1\right|-\left|\sqrt{7}-1\right|\)
\(\sqrt{2}.B=\sqrt{7}+1-\sqrt{7}+1\)
\(\sqrt{2}.B=2\)
\(B=\dfrac{2}{\sqrt{2}}\)
\(B=\sqrt{2}\)
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\(B=\sqrt{4}-\sqrt{4}+-\sqrt{7}+\sqrt{7}=0+0=0\)
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