Rút gọn biểu thức: D =frac2( a + b )sqrt b sqrtfrac b a 2+2 ab + b 2 vói a , b

$D=\frac{2(a+b)}{\sqrt{b}} \sqrt{\frac{b}{a^{2}+2 a b+b^{2}}}$

$=\frac{2(a+b)}{\sqrt{b}} \cdot \frac{\sqrt{b}}{\sqrt{a^{2}+2 a b+b^{2}}}$

$=\frac{2(a+b)}{\sqrt{b}} \cdot \frac{\sqrt{b}}{\sqrt{(a+b)^{2}}}$