Question

A-(√12-15).(√12+15)

B-(√8+√10).(√8+√10)


C-(√7+19).(√7-19)

Answer 1

$a) \: ( \sqrt{12} - 15) \times ( \sqrt{12} + 15) \\ (\sqrt{12} \times \sqrt{12}) + (15 \times \sqrt{12}) - (15 \times \sqrt{12}) - 15 \times 15 \\ 12 - 225 \\ - 213$

$b)( \sqrt{8} + \sqrt{10}) \times ( \sqrt{8} + \sqrt{10}) \\ ( \sqrt{8} \times \sqrt{8}) + ( \sqrt{8} \times \sqrt{10}) + ( \sqrt{10} \times \sqrt{8}) + ( \sqrt{10} \times \sqrt{10}) \\ 8 + \sqrt{80} + \sqrt{80} + 10 \\ 18 + 2 \sqrt{80} \\ 18 + 2(4 \sqrt{5}) \\ 18 + 8 \sqrt{5}$

$c)( \sqrt{7} + 19) \times ( \sqrt{7} - 19) \\ ( \sqrt{7} \times \sqrt{7}) + ( \sqrt{7} \times ( - 19)) + (19 \times \sqrt{7}) + (19 \times ( - 19)) \\ 7 - 19 \sqrt{7} + 19 \sqrt{7} - 361 \\ - 361 + 7 \\ - 354$