a) \(\eqalign{
& \sqrt {75} + \sqrt {48} - \sqrt {300} \cr
& = \sqrt {25.3} + \sqrt {16.3} - \sqrt {100.3} \cr} \)
\( = 5\sqrt 3 + 4\sqrt 3 - 10\sqrt 3 = - \sqrt 3 \)
b)\(\eqalign{
& \sqrt {98} - \sqrt {72} + 0,5\sqrt 8 \cr
& = \sqrt {49.2} - \sqrt {36.2} + 0,5\sqrt {4.2} \cr} \)
\( = 7\sqrt 2 - 6\sqrt 2 + \sqrt 2 = 2\sqrt 2 \)
c)\(\eqalign{
& \sqrt {9a} - \sqrt {16a} + \sqrt {49a} \cr
& = 3\sqrt a - 4\sqrt a + 7\sqrt a \cr
&= 6\sqrt a \,(với \, a\ge 0)\cr} \)
d)\(\eqalign{
& \sqrt {16b} + 2\sqrt {40b} - 3\sqrt {90b} \cr
& = \sqrt {16b} + 2\sqrt {4.10b} - 3\sqrt {9.10b} \cr} \)
\(\eqalign{
& = 4\sqrt b + 4\sqrt {10b} - 9\sqrt {10b} \cr
& = 4\sqrt b - 5\sqrt {10b} \,\,(với \, b \ge 0)\cr} \)
