P(A) = 0,2; P(A ngang) = 0,8. P(B) = 0,3; P(B ngang) = 0,7. a) Bien co "Lan 1 trung, lan 2 khong trung" la (A ngang giao B): P = 0,8 * 0,3 = 0,24. b) Bien co "Co it nhat mot lan trung" la 1 tru di "Ca hai lan truot": P = 1 - (0,2 * 0,3) = 0,94. Dap so: a) 0,24; b) 0,94.

Dat t = 2^x (t > 0). ​Phuong trinh: t^2 - 12t + m = 0. ​De co 2 nghiem phan biet: Delta' = 36 - m > 0 va m > 0 => 0 < m < 36. ​Theo de bai: x1 + x2 = 5. ​Suy ra: 2^x1 * 2^x2 = 2^5 = 32. ​Theo Vi-et: t1 * t2 = m. ​Vay m = 32 (thoa man dieu kien). Dap so: m = 32.

​SA vuong goc (ABCD). ​Khoang cach tu D den (SBM) bang khoang cach tu A den (SBM). ​Ke AK vuong goc BM, AH vuong goc SK. Khoang cach la AH. ​BM = (a * can 5) / 2. ​Dien tich tam giac ABM = (a^2) / 2. ​AK = (2 * Dien tich ABM) / BM = 2a / can 5. ​1/AH^2 = 1/SA^2 + 1/AK^2 = 1/(4a^2) + 5/(4a^2) = 6/(4a^2). ​AH = (a * can 6) / 3. Dap so: (a * can 6) / 3.