Giải thích các bước giải:
`a)`
`sqrt{9a}+sqrt{25a}-sqrt{49a}` với `age0`
`=sqrt{3^2 a}+sqrt{5^2 a}-sqrt{7^2 a}`
`=3sqrt{a}+5sqrt{a}-7sqrt{a}`
`=(3+5-7)sqrt{a}`
`=sqrt{a}`
`b)`
`sqrt{75}+sqrt{48}-sqrt{300}`
`=sqrt{25.3}+sqrt{16.3}-sqrt{100.3}`
`=sqrt{5^2 .3}+sqrt{4^2 .3}-sqrt{10^2 .3}`
`=5sqrt{3}+4sqrt{3}-10sqrt{3}`
`=(5+4-10)sqrt{3}`
`=-sqrt{3}`
`c)`
`(2sqrt{3}+sqrt{5})sqrt{3}-sqrt{60}`
`=2sqrt{3}.sqrt{3}+sqrt{5}.sqrt{3}-sqrt{60}`
`=2sqrt{3^2}+sqrt{5.3}-sqrt{60}`
`=2.3+sqrt{15}-sqrt{4.15}`
`=6+sqrt{15}.1-sqrt{2^2 .15}`
`=6+sqrt{15}.1-2sqrt{15}`
`=6+(1-2)sqrt{15}`
`=6-sqrt{15}`