Bài 6 :
\(A=\sqrt{a^2+6a+9}+\sqrt{a^2-6a+9}\) với \(-3\le a\le3\)
\(A=\sqrt{\left(a+3\right)^2}+\sqrt{\left(a-3\right)^2}\)
\(A=\left|a+3\right|+\left|a-3\right|\)
\(A=a+3-\left(a-3\right)\)
\(A=a+3-a+3=6\)
\(B=\sqrt{a+2\sqrt{a-1}}+\sqrt{a-2\sqrt{a-1}}\) với \(1\le a\le2\)
\(B=\sqrt{\left(\sqrt{a-1}\right)^2+2\sqrt{a-1}+1}+\sqrt{\left(\sqrt{a-1}\right)^2-2\sqrt{a-1}+1}\)
\(B=\sqrt{\left(\sqrt{a-1}+1\right)^2}+\sqrt{\left(\sqrt{a-1}-1\right)^2}\)
\(B=\left|\sqrt{a-1}+1\right|+\left|\sqrt{a-1}-1\right|\)
\(B=\sqrt{a-1}+1-\sqrt{a-1}+1\)
\(B=2\)
Đúng 3
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