MC vdi (O) (C la tiep diem) Ke CH vuong goc vdi AB (He AB), MB cat
b) Giatri cu aA khi x =9 la c) V d i X > 0, X 5^ 25 (*)
V9 + 5 3 + 5 8 A < - < = > ^ : ^ — ^ < - < = > 3 N / X - 1 5 < Vx + 5 o 2> / x < 2 0 3 ^ + 5 3 <=> Vx < 1 0 o O< x < 100. Ket hdp (*), ta CO A < ^ o 0 < x < 100 va x 2. N h a n x e t :
1) LiTu y rang X - 25 = (Vx + 5)(Vx - 5) vdi x > 0. 2) Giai bat phiTdng trinh dang V A < B, can nhd ring : 2) Giai bat phiTdng trinh dang V A < B, can nhd ring :
V A < B o A > 0 B > 0 , V A < B <=> . A < B^ A > 0 B > 0 A < B^
Bai 2: Goi so ngay theo ke hoach dpi xe chd het hang la x (ngay) (Dieu kien x e N*)
140
Theo ke hoach m o i ngay dpi xe chd la : 140 : x = (tan hang)
X
So ngay theo thiTc te dpi xe chd hang la : x - 1 (ngay) Thifc te dpi xe chd diTdc 1^ : 140 + 10 = 150 (tan hang)
Cty TNHH MTV DWH Khang Vi$t
Theo thifc té m o i ngay dpi xe chd la : 150 : (x - 1) = Theo dau bai ta c6 phÚdng trinh : 150 140
X - 1 = 5<=> 150 150 X - 1 30 x- 1 (tan hang) ^ 30x - 28x + 28 = x^ - X x^ - 3x - 28 = 0 A = 9 + 1 1 2 = 1 2 1, 7A = 11 3
' ^ = 7 (thich hdp) ; X2 = -—^ = - 4 (khong thich hPp)
2 2
Vay theo ke hoach dpi xe chd het hang trong 7 ngaỵ
Nhan x e t : Giai bai loan bang each lap phúring trinh, he phufdng trinh ve
nang suát. Lu\ y rang : thiTc té - dif dinh - hrin (kem) Hoac Dir dinh - thi/c te = hdn (kem)
B a i 3 : a ) ( d ) k h i m = 1 l a y = 2x + 8 - ' Phifdng trinh hoanh dp giao diem cija (P) va (d) khi m = 1 la :
x^ = 2x + 8 o x ' - 2x - 8 = 0 ^ A ' = 1 + 8 = 9 ; V A " = 3 1 + 3 , 1 - 3
=> x, = - y - = 4 ; X2 = — ^ = - 2 .
• x, = 4 t h i y , = 4 ^ = 16 • X j = - 2 thi ya = (-2)^ = 4
Vay tpa dp giao diem cua (P) va (d) khi m = 1 la (4 ; 16) va (-2 ; 4). b) Phúring trinh hoanh dp giao diem cua (P) va (d) la :
x^ = 2x - m^ + 9 x^ - 2x + m^ - 9 = 0 (*) (d) cat (P) tai hai diem n^m ve hai phia cua true tung o (*) CO hai nghiem phan biet trai dáu <=> a va c trai dáu <=>ac = m^ - 9 < 0 o m ^ < 9 o | m | < 3 o - 3 < m < 3
Nhan x e t :
1) (d) c^t (P) tai hai diem n i m ve hai phia cua true tung k h i va chi khi phiTring trinh hoanh dp giao diem c6 hai nghiem phan biet trai daụ