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Tìm đa thức M biết :
a, M +5 (5x2 - 2xy) = 6x2 +9xy - y2
M + 5. 5x2 - 5. 2xy = 6x2 + 9xy - y2
M + 25x2 - 10xy = 6x2 + 9xy - y2
M = 6x2 + 9xy - y2 + 10xy - 25x2
M = ( 6x2 - 25x2 ) + ( 9xy + 10xy ) - y2
M = -19x2 + 19xy - y2
b, M - ( 3xy - 4y2 ) = x2 - 7xy + 8xy
M - 3xy + 4y2 = x2 - 15xy
M = x2 - 15xy - 4y2 + 3xy
M = x2 + ( 15xy + 3xy ) - 4y2
M = x2 + 18xy - 4y2
c, (25 . x2y - 13xy2+ y3 ) - M = 11x2y - 2y3
25x2y - 13xy2+ y3 - M = 11x2y - 2y3
M = 25x2y - 13xy2+ y3 - 11x2y - 2y3
M = ( 25x2y - 11x2y ) + ( y3 - 2y3 ) - 13xy2
M = 14x2y - y3 - 13xy2
d, M + (5x2 - 2xy )= 6x2 + 9xy -y2
M + 5x2 - 2xy = 6x2 + 9xy -y2
M = 6x2 + 9xy -y2 + 2xy - 5x2
M = ( 6x2 - 5x2 ) + ( 9xy + 2xy ) - y2
M = x2 + 11xy - y2
Có M+5x^2-2xy-y^2=6x^2+9xy-y^2
=> M= 6x^2+9xy-y^2-(5x^2-2xy-y^2)
=> M=6x^2-9xy-y^2-5x^2+2xy+y^2
=>M=(6x^2-5x^2)+(-9xy+2xy)+(y^2-y^2)
=> M= x^2-7xy
M + 5x2 - 2xy - y2 = 6x2 + 9xy - y2
=> M = (6x2 + 9xy - y2) - ( 5x2 - 2xy - y2 ) (chuyển vế)
=> M = 6x2 + 9xy - y2 - 5x2 + 2xy + y2 ( bỏ dấu ngoặc)
=> M = ( 6x2 - 5x2) + (9xy + 2xy) + ( - y2 + y2)
=> M = x2 + 11xy
Bài 1 :
A + B = 4x2 - 5xy + 3y2 + 3x2 + 2xy - y2
= ( 4x2 + 3x2 ) - ( 5xy - 2xy ) + ( 3y2 - y2 )
= 7x2 - 3xy + 2y2
A - B = 4x2 - 5xy + 3y2 - ( 3x2 + 2xy - y2 )
= 4x2 - 5xy + 3y2 - 3x2 - 2xy + y2
= ( 4x2 - 3x2 ) - ( 5xy + 2xy ) + ( 3y2 + y2 )
= x2 - 7xy + 4y2
Bài 2 :
a) M + (5x2 - 2xy) = 6x2 + 9xy - y2
M = 6x2 + 9xy - y2 - (5x2 - 2xy)
M = 6x2 + 9xy - y2 - 5x2 + 2xy
M = ( 6x2 - 5x2 ) + ( 9xy + 2xy ) - y2
M = x2 + 11xy - y2
Vậy M = x2 + 11xy - y2
b) (3xy - 4y2) - N = x2 - 7xy + 8y2
N = 3xy - 4y2 - x2 - 7xy + 8y2
N = ( 3xy - 7xy ) - ( 4y2 - 8y2 ) - x2
N = -4xy + 4y2 - x2
Vậy N = -4xy + 4y2 - x2
3, Cho đa thức
A(x)+B(x) = (3x4-\(\dfrac{3}{4}\)x3+2x2-3)+(8x4+\(\dfrac{1}{5}\)x3-9x+\(\dfrac{2}{5}\))
= 3x4-\(\dfrac{3}{4}\)x3+2x2-3+8x4+\(\dfrac{1}{5}\)x3-9x+\(\dfrac{2}{5}\)
= (3x4+8x4)+(-3/4x3+1/5x3)+(-3+2/5)+2x2-9x
= 11x4 -0.55x3-2.6+2x2-9x
A(x)-B(x)=(3x4-\(\dfrac{3}{4}\)x3+2x2-3)-(8x4+\(\dfrac{1}{5}\)x3-9x+\(\dfrac{2}{5}\))
= 3x4-\(\dfrac{3}{4}\)x3+2x2-3-8x4-\(\dfrac{1}{5}\)x3+9x-\(\dfrac{2}{5}\)
= (3x4-8x4)+(-3/4x3-1/5x3)+(-3-2/5)+2x2+9x
= -5x4-0.95x3-3.4+2x2+9x
B(x)-A(x)=(8x4+\(\dfrac{1}{5}\)x3-9x+\(\dfrac{2}{5}\))-(3x4-\(\dfrac{3}{4}\)x3+2x2-3)
=8x4+\(\dfrac{1}{5}\)x3-9x+\(\dfrac{2}{5}\)-3x4+\(\dfrac{3}{4}\)x3-2x2+3
=(8x4-3x4)+(1/5x3+3/4x3)+(2/5+3)-9x-2x2
= 5x4+0.95x3+2.6-9x-2x2
a) M + (5x2 - 2xy) = 6x2 + 9xy - y2
=> M = (6x2 + 9xy - y2) - (5x2 - 2xy)
=> M = 6x2 + 9xy - y2 - 5x2 + 2xy = x2 + 11xy - y2
b) (25x2y - 13xy2 + y3) - m = 11x2y - 2y3
=> m = (25x2y - 13xy2 + y3) - (11x2y - 2y3)
=> m = 25x2y - 13xy2 + y3 - 11x2y + 2y3 = 14x2y - 13xy2 + 3y3
c) M = 0 - (12x4 - 15x2y + 2xy2 + 7) = -12x4 + 15x2y - 2xy2 - 7
a,\(M+\left(5x^2-2xy\right)=6x^2+9xy-y^2\)
\(< =>M=6x^2+9xy-y^2-5x^2+2xy\)
\(< =>M=x^2+11xy-y^2\)
b,\(\left(25x^2y-13xy^2+y^3\right)-M=11x^2y-2y^3\)
\(< =>M=25x^2y-13xy^2+y^3-11x^2y+2y^3\)
\(< =>M=14x^2y-12xy^2+3y^3\)
c,\(M+\left(12x^4-15x^2y+2xy^2+7\right)=0\)
\(< =>M=15x^2y-7-2xy^2-12x^4\)
a) A+\(\left(x^2-4xy^2+2xz-3y^2\right)\)=0
=> A=0-\(\left(x^2-4xy^2+2xz-3y^2\right)\)
=>A=\(-x^2+4xy^2-2xz+3xy^2\)
b)B+\(\left(5x^2-2xy\right)=6x^2+9xy-y^2\)
=>B=\(6x^2+9xy-y^2-\left(5x^2-2xy\right)\)
=>B=\(6x^2+9xy-y^2-5x^2+2xy\)
=>B=\(\left(6x^2-5x^2\right)+\left(9xy+2xy\right)-y^2\)
=>B=\(x^2+11xy-y^2\)
c)ta có:
B+(\(4x^2y+5y^2-3xz+z^2\))
thay B=\(x^2+11xy-y^2\) vào biểu thức trên ta được:
\(x^2+11xy-y^2\) + (\(4x^2y+5y^2-3xz+z^2\))
= \(x^2+11xy-y^2+4x^2y+5y^2-3xz+z^2\)
=\(\left(5y^2-y^2\right)+x^2+11xy-y^2+4x^2y+5y^2-3xz+z^2\)
=\(4y^2+x^2+11xy-y^2+4x^2y+5y^2\)
đúng chưa bạn
a) A + (x\(^2\) - 4xy\(^2\) + 2xz - 3y\(^2\) ) = 0
(=) A = -x\(^2\) +4xy\(^2\) - 2xz + 3y\(^2\)
b) B + (5x\(^2\) - 2xy) = 6x\(^2\) + 9xy - y\(^2\)
(=) B = 6x\(^2\) + 9xy - y\(^2\) - 5x\(^2\) + 2xy
(=) B = x\(^2\) + 11xy - y\(^2\)
c) Đa thức không chứa biến x là 5 ( có thể thay đổi )
(=) B + (4x\(^2\)y + 5y\(^2\) - 3xz + z\(^2\)) = 5
(=) B = 5 - 4x\(^2\)y - 5y\(^2\) + 3xz - z\(^2\)
1. A+(x2-4xy2+2xz-3y2) =0
=> A = -(x2-4xy2+2xz-3y2)
=> A = -x2+4xy2-2xz+3y2
Vậy A=-x2+4xy2-2xz+3y2
M+(5x2-2xy)=6x2+9xy-y2
=>M=(6x2+9xy-y2)-(5x2-2xy)
=6x2+9xy-y2-5x2+2xy
=x2+11xy-y2
Vậy M=x2+11xy-y2
M + ( 5x2 -2xy) = 6x2 + 9xy -y2
M = 6x2 + 9xy -y2 - ( 5x2 -2xy)
M = x2 + 11xy - y2
Vũ Minh Tuấn,Băng Băng 2k6
1)
\(M+\left(5x^2-2xy\right)=6x^2+9xy-y^2\)
\(M+5x^2-2xy=6x^2+9xy-y^2\)
\(M=\left(6x^2+9xy-y^2\right)-\left(5x^2+2xy\right)\)
\(M=6x^2+9xy-y^2-5x^2-2xy\)
\(M=\left(6x^2-5x^2\right)+\left(9xy-2xy\right)-y^2\)
\(M=x^2+7xy-y^2.\)
Chúc em học tốt!