thu gọn : A= (3 + căn 5)(căn 10-căn 2). căn 3 trừ căn 5(căn của cả 3 và căn 5 nhé)

`A=(3 + sqrt(5))(sqrt(10) - sqrt(2)) * sqrt(3 - sqrt(5))`$\\$`=(3sqrt(10) - 3sqrt(2) + sqrt(50) - sqrt(10)) * sqrt(3 - sqrt(5))`$\\$`=(3sqrt(10) - 3sqrt(2) + 5sqrt(2) - sqrt(10)) * sqrt(3 - sqrt(5))`$\\$`=(2sqrt(10) + 2sqrt(2)) * sqrt(3 - sqrt(5))`$\\$`=2sqrt(10(3 - sqrt(5))) + 2sqrt(2(3 - sqrt(5)))`$\\$`=2sqrt(30 - 10sqrt(5)) + 2sqrt(6 - 2sqrt(5))`$\\$`=2sqrt((5 - sqrt(5)) ^ 2) + 2sqrt((1 - sqrt(5)) ^ 2)`$\\$`=2(5 - sqrt(5)) + 2(sqrt(5) - 1)`$\\$`=10 - 2sqrt(5) + 2sqrt(5) - 2`$\\$`=10-2`$\\$`=8`