Question

1) PTTNT

a) x^2 - 4x^2y + 4xy

b)x^2 + 3x + x - 3y

2) Tim GTLN

-2x^2 + 3x - 5

3) tim x,y thuoc z

3xy + 6x - y = 7

Answer 1

Bài 2:

\(A=-2x^2+3x-5\)

\(=-2\left(x^2+\frac{3x}{2}-\frac{5}{2}\right)\)

\(=-2\left(x^2-\frac{3x}{2}+\frac{9}{16}\right)-\frac{31}{8}\)

\(=-2\left(x-\frac{3}{4}\right)^2-\frac{31}{8}\le-\frac{31}{8}\)

Dấu = khi \(-2\left(x-\frac{3}{4}\right)^2=0\Leftrightarrow x-\frac{3}{4}=0\Leftrightarrow x=\frac{3}{4}\)

Vậy \(Max_A=-\frac{31}{8}\Leftrightarrow x=\frac{3}{4}\)

Answer 2

Bài 1:

a)x²-4x²y+4xy

=x(x-4xy+y)

b)đề sai

Answer 3

Bài 3:

3yx + 6x - y = 7

<=> x(3y+6) - (3y+6) = 27

<=> (3y+6)(x+1) = 27

Ta có bảng sau:

x+1		1	-1	3	-3	9	-9	27	-27
3y+6		27	-27	9	-9	3	-3	1	-1
x		0	-2	2	-4	8	-10	26	-28
y		7	-11	1	-5	-1	-3	\(-\frac{5}{3}\)	\(-\frac{7}{3}\)

Vậy...