Tìm GTLN của :
a) A= -4x^2 + x - 3
b) B= -5x^2 -7x + 9
c) C= -3x^2 + 2x
a)
A = . . . . . = − ( 4 x 2 − x + 1 16 ) − 47 16 = − ( 2 x − 1 4 ) 2 − 47 16 ≤ − 47 16 A=.....=-(4x^{2}-x+\frac{1}{16})-\frac{47}{16} = -(2x-\frac{1}{4})^{2}-\frac{47}{16} \leq -\frac{47}{16} A = . . . . . = − ( 4 x 2 − x + 1 6 1 ) − 1 6 4 7 = − ( 2 x − 4 1 ) 2 − 1 6 4 7 ≤ − 1 6 4 7
b)
B = . . . . . . . = − 1 5 ( x + 7 10 ) 2 + 9 , 49 ≤ 9 , 49 B=.......=-\frac{1}{5}(x+\frac{7}{10})^{2}+9,49 \leq 9,49 B = . . . . . . . = − 5 1 ( x + 1 0 7 ) 2 + 9 , 4 9 ≤ 9 , 4 9
c)
3 C = − 9 x 2 + 6 x = − [ ( 3 x ) 2 − 2.3 x . 1 + 1 ] + 1 = − ( 3 x − 1 ) 2 + 1 ≤ + 1 3C=-9x^{2}+6x=-[(3x)^{2}-2.3x.1+1]+1 = -(3x-1)^{2}+1 \leq +1 3 C = − 9 x 2 + 6 x = − [ ( 3 x ) 2 − 2 . 3 x . 1 + 1 ] + 1 = − ( 3 x − 1 ) 2 + 1 ≤ + 1
=>
M A X C = 1 3 MAX_{C} = \frac{1}{3} M A X C = 3 1
Last edited: 22 Tháng bảy 2020