`1.56`
`a)` Ta có:
`2sqrt{5}=sqrt{2^2 .5}=sqrt{4.5}=sqrt{20}`
`2sqrt{6}=sqrt{2^2 .6}=sqrt{4.6}=sqrt{24}`
`3sqrt{5}=sqrt{3^2 .5}=sqrt{9.5}=sqrt{45}`
Mà: `sqrt{20}<sqrt{24}<sqrt{29}<sqrt{45}`
Vậy `2sqrt{5};2sqrt{6};sqrt{29};3sqrt{5}.`
`b)`Ta có:
`3sqrt{6}=sqrt{3^2 .6}=sqrt{9.6}=sqrt{54}`
`3sqrt{3}=sqrt{3^2 .3}=sqrt{9.3}=sqrt{27}`
`4sqrt{7}=sqrt{4^2 .7}=sqrt{16.7}=sqrt{112}`
Mà: `sqrt{20}<sqrt{24}<sqrt{29}<sqrt{45}`
`2sqrt{14}=sqrt{2^2 .14}=sqrt{4.14}=sqrt{56}`
Mà: `sqrt{27}<sqrt{54}<sqrt{56}<sqrt{112}`
Vậy `3sqrt{3};3sqrt{6};2sqrt{14};4sqrt{7}.`
`1.57`
`a)sqrt{75}+sqrt{48}-sqrt{300}`
`=sqrt{5^2 .3}+sqrt{4^2 .3}-sqrt{10^2. 3}`
`=5sqrt{3}+4sqrt{3}-10sqrt{3}`
`=-sqrt{3}`
`b)sqrt{98}-sqrt{72}+0,5sqrt{8}`
`=sqrt{7^2 .2}-sqrt{6^2 .2}+sqrt{0,25.8}`
`=7sqrt{2}-6sqrt{2}+sqrt{2}`
`=2sqrt{2}`
`c)sqrt{9a}-sqrt{16a}+sqrt{49a}`
`=sqrt{3^2 .a}-sqrt{4^2 .a}+sqrt{7^2 .a}`
`=3sqrt{a}-4sqrt{a}+7sqrt{a}`
`=6sqrt{a}`
`d)sqrt{160b}+2sqrt{40b}-3sqrt{90b}`
`=sqrt{4^2 .10b}+2sqrt{2^2. 10b}-3sqrt{3^2. 10b}`
`=4sqrt{10b}-2.2sqrt{10b}-3.3sqrt{10b}`
`=4sqrt{10b}-4sqrt{10b}-9sqrt{10b}`
`=-9sqrt{10b}.`
