Đáp án:
`1)`
`A=\sqrt{45}+\sqrt{245}-\sqrt{80}`
`=\sqrt{5.9}+\sqrt{5.49}-\sqrt{5.16}`
`=\sqrt{5.3^{2}}+\sqrt{5.7^{2}}-\sqrt{5.4^{2}}`
`=3\sqrt{5}+7\sqrt{5}-4\sqrt{5}`
`=6\sqrt{5}`
Vậy `A=6\sqrt{5}`
`3)`
`A=5\sqrt{8}+\sqrt{50}-2\sqrt{18}`
`=5.2\sqrt{2}+\sqrt{5^{2}.2}-2.\sqrt{2.3^{2}}`
`=10\sqrt{2}+5\sqrt{2}-2.3\sqrt{2}`
`=15\sqrt{2}-6\sqrt{2}`
`=9\sqrt{2}`
Vậy `B=9\sqrt{2}`
`4)`
`A=\sqrt{27}-2\sqrt{12}-\sqrt{75}`
`=\sqrt{3.3^{2}}-2.\sqrt{3.2^{2}}-\sqrt{3.5^{2}}`
`=3\sqrt{3}-2.2\sqrt{3}-5\sqrt{3}`
`=-2\sqrt{3}-4\sqrt{3}`
`=-6\sqrt{3}`
Vậy `A=-6\sqrt{3}`
`5)`
`A=\sqrt{12}+\sqrt{27}-\sqrt{48}`
`=\sqrt{3.2^{2}}+\sqrt{3.3^{2}}-\frac{3.4^{2}}`
`=2\sqrt{3}+3\sqrt{3}-4\sqrt{3}`
`=\sqrt{3}`
Vậy `A=\sqrt{3}`
`6)`
`B=2\sqrt{3}+3\sqrt{27}-\sqrt{300}`
`=2\sqrt{3}+3.\sqrt{3.3^{2}}-\sqrt{3.10^{2}}`
`=2\sqrt{3}+3.3\sqrt{3}-10\sqrt{3}`
`=-8\sqrt{3}+9\sqrt{3}`
`=\sqrt{3}`
Vậy `B=\sqrt{3}`
`7)`
`A=3\sqrt{2}+4\sqrt{18}`
`=3\sqrt{2}+4.\sqrt{2.3^{2}}`
`=3\sqrt{2}+4.3\sqrt{2}`
`=3\sqrt{2}+12\sqrt{2}`
`=15\sqrt{2}`
vậy `A=15\sqrt{2}`
`8)`
`A=2\sqrt{3}-4\sqrt{27}+5\sqrt{48}`
`=2\sqrt{3}-4.\sqrt{3.3^{2}}+5.\sqrt{3.4^{2}}`
`=2\sqrt{3}-4.3\sqt{3}+5.4\sqrt{3}`
`=2\sqrt{3}-12\sqrt{3}+20\sqrt{3}`
`=10\sqrt{3}`
Vậy `A=10\sqrt{3}`
