Question

rút gọn

a, \(\sqrt{12-2\sqrt{11}}-\sqrt{11}\)

b, \(x-4+\sqrt{16-8x+x^2}\left(x>4\right)\)

c, \(\sqrt{3-2\sqrt{2}+}\sqrt{3+2\sqrt{2}}\)

d, \(A=\dfrac{a\sqrt{a}-8+2a-4\sqrt{a}}{a-4}\)

Answer 1

a ) \(\sqrt{12-2\sqrt{11}}-\sqrt{11}=\sqrt{11}-1-\sqrt{11}=-1\)

b ) \(x-4+\sqrt{16-8x+x^2}\left(x>4\right)\)

\(=x-4+x-4=-8\)

c ) \(\sqrt{3-2\sqrt{2}}+\sqrt{3+2\sqrt{2}}=\sqrt{2}-1+\sqrt{2}+1=2\sqrt{2}\)

Answer 2

a,

\(\sqrt{12-2\sqrt{11}}-\sqrt{11}\\ =\sqrt{\left(\sqrt{11}-1\right)^2}-\sqrt{11}\\ =\left|\sqrt{11}-1\right|-\sqrt{11}\\ =\sqrt{11}-1-\sqrt{11}\\ =-1\)

b,

\(x-4+\sqrt{16-8x+x^2}\\ =x-4+\sqrt{\left(4-x\right)^2}\\ =x-4+\left|4-x\right|\\ =x-4+x-4\\ =2x-8\\ =2\left(x-4\right)\)

c,

\(\sqrt{3-2\sqrt{2}}+\sqrt{3+2\sqrt{2}}\\ =\sqrt{\left(\sqrt{2}-1\right)^2}+\sqrt{\left(\sqrt{2}+1\right)^2}\\ =\left|\sqrt{2}-1\right|+\left|\sqrt{2}+1\right|\\ =\sqrt{2}-1+\sqrt{2}+1\\ =2\sqrt{2}\)

d,

\(A=\dfrac{a\sqrt{a}-8+2a-4\sqrt{a}}{a-4}\\ =\dfrac{\left(a\sqrt{a}-4\sqrt{a}\right)+\left(2a-8\right)}{a-4}\\ =\dfrac{\left(a-4\right)\sqrt{a}+2\left(a-4\right)}{a-4}\\ =\dfrac{\left(a-4\right)\left(\sqrt{a}+2\right)}{\left(a-4\right)}\\ =\sqrt{a}+2\)