Đáp án+Giải thích các bước giải:

 `a)`

`(\sqrt{7}+\sqrt{3})^{2}`

`=(\sqrt{7})^{2}+2.\sqrt{7}.\sqrt{3}+(\sqrt{3})^{2}`

`=7+2\sqrt{21}+3`

`=10+2\sqrt{21}`

`b)`

`(\sqrt{11}-\sqrt{5})^{2}`

`=(\sqrt{11})^{2}-2.\sqrt{11}.\sqrt{5}+(\sqrt{5})^{2}`

`=11-2\sqrt{55}+5`

`=16-2\sqrt{55}`

`c)`

`(\sqrt{13}+\sqrt{7})^{2}`

`=(\sqrt{13})^{2}+2.\sqrt{13}.\sqrt{7}+(\sqrt{7})^{2}`

`=13+2\sqrt{91}+7`

`=20+2\sqrt{91}`

`d)`

`(\sqrt{x}+\sqrt{y})^{2}(đk:x,y\ge0)`

`=(\sqrt{x})^{2}+2.\sqrt{x}.\sqrt{y}+(\sqrt{y})^{2}`

`=x+2\sqrt{xy}+y`

`e)`

`(\sqrt{a}-\sqrt{b})^{2}(đk:a,b\ge0)`

`=(\sqrt{a})^{2}-2.\sqrt{a}.\sqrt{b}+(\sqrt{b})^{2}`

`=a-2\sqrt{ab}+b`

`f)`

`(\sqrt{c}+\sqrt{d})^{2}(đk:c,d\ge0)`

`=(\sqrt{c})^{2}+2.\sqrt{c}.\sqrt{d}+(\sqrt{d})^{2}`

`=c+2\sqrt{cd}+d`