M (-1 + T; T; -9 + 6T) ∈∆1; ∆2 QUA A (1; 3; -1) COỰ VEỰCTỤ CHỔ PHỬỤ...

2. M (-1 + t; t; -9 + 6t) ∈∆

1

; ∆

2

qua A (1; 3; -1) coự veựctụ chổ phửụng ar= (2; 1; -2) = (t – 2; t – 3; 6t – 8) ⇒ AM auuuur r∧ = (14 – 8t; 14t – 20; 4 – t)AMuuuurTa coự : d (M, ∆

2

) = d (M, (P)) ⇔ 261t

²

−792t 612+ =11t 20−⇔ 35t

²

- 88t + 53 = 0 ⇔ t = 1 hay t = 5335 Vaọy M (0; 1; -3) hay M 18 53 3; ; ữ35 35 35 Caõu VII.b. ẹieàu kieọn x, y > 0 + = + =

2

2

log (x y ) log 2 log (xy) log (2xy)

2

2

2

2

− + =x xy y 4 = − = + = − =x y 2xy(x y)

2

0⇔  = − = ⇔ x y = ⇔ x 2 = hay x 2xy 4y 2 ⇔ Ths. Leõ Ngoõ Thieọn (Phoự chuỷ nhieọm khoa Toaựn – ẹH Sử Phaùm TP.HCM)