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a/ \(A=20x^3-10x^2+5x-20x^3+10x^2+4x=9x\)
Thay x = 15 vào bt A ta có
A = 9 . 15 = 135
b/ \(B=5x^2-20xy-4y^2+2xy=5x^2-4y^2\)
Thay x = -1/5 ; y = - 1/2 vào bt B ta có
\(B=5.\dfrac{1}{25}-4.\dfrac{1}{4}=\dfrac{1}{5}-1=-\dfrac{4}{5}\)
c/ \(C=6x^2y^2-6xy^3-8x^3+8x^2y^2-5x^2y^2+5xy^3\)
\(=9x^2y^2-xy^3-8x^3\)
Thay x = 1/2 ; y = 2 vào bt C ta có
\(C=9.4.\dfrac{1}{4}-\dfrac{1}{2}.8-8.\dfrac{1}{8}=9-4-1=4\)
d/ \(D=6x^2+10x-3x-5+6x^2-3x+8x-2\)
\(=12x^2+12x-3\)
\(\left|x\right|=2\Rightarrow x=\pm2\)
Thay x = 2 vào bt D có
\(D=12.4+12.2-3=69\)
Thay x = - 2 vào bt D ta có
\(D=12.4-12.2-3=21\)
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1/
a/ \(D=2x\left(10x^2-5x-2\right)-5x\left(4x^2-2x-1\right)\)
\(D=2x\left[10\left(x^2-\frac{1}{2}x-\frac{1}{5}\right)\right]-5x\left[4\left(x^2-\frac{1}{2}x-\frac{1}{4}\right)\right]\)
\(D=20x\left(x^2-\frac{1}{2}x-\frac{1}{5}\right)-20x\left(x^2-\frac{1}{2}x-\frac{1}{4}\right)\)
\(D=20x^3-10x^2-4x-20x^3+10x^2+5x\)
\(D=x\)
b/ Mình xin sửa lại đề:
Tính giá trị biểu thức \(E\left(x\right)=x^5-13x^4+13x^3-13x^2+13x+2012\)
Tại x = 12
\(E\left(x\right)=x^5-\left(x+1\right)x^4+\left(x+1\right)x^3-\left(x+1\right)x^2+\left(x-1\right)x+2012\)
\(E\left(x\right)=x^5-x^5-x^4+x^4+x^3-x^3-x^2+x^2-x+2012\)
\(E\left(x\right)=2012-x\)
\(E\left(x\right)=2000\)
2/
a/ \(2x\left(x-5\right)-x\left(3+2x\right)=26\)
<=> \(2x^2-10x-3x-2x^2=26\)
<=> \(-13x=26\)
<=> \(x=-2\)
b/ Bạn vui lòng coi lại đề.
3a/ Ta có \(D=x\left(5x-3\right)-x^2\left(x-1\right)+x\left(x^2-6x\right)-10+3x\)
\(D=5x^2-3x-x^3+x^2+x^3-6x^2-10+3x\)
\(D=-10\)
Vậy giá trị của D không phụ thuộc vào x (đpcm)
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bài 1:
a. \((x+1)(x+3) - x(x+2)=7 \)
\(x^2+ 3x +x +3 - x^2 -2x =7\)
\(x^2+4x+3-x^2-2x=7\)
\(=> 2x+3=7\)
\(2x=4\)
\(x = 2\)
Bài 2:
a)
\((3x-5)(2x+11) -(2x+3)(3x+7) \)
\(= 6x^2 +33x-10x-55-6x^2-14x-9x-10\)
\(= (6x^2-6x^2)+(33x-10x-14x-9x)-(55+10)\)
\(=-65\)
\(\)
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a) \(A=5x\left(4x^2-2x+1\right)-2x\left(10x^2-5x-2\right)\)
\(A=20x^3-10x^2+5x-20x^3+10x^2+4x\)
\(A=9x\)
Thay x = 15 vào, ta có:
\(A=9.15=135\)
b) \(B=5x\left(x-4y\right)-4y\left(y-5x\right)\)
\(B=5x^2-20xy-4y^2+20xy\)
\(B=5x^2-4y\)
Thay \(x=-\frac{1}{5};y=-\frac{1}{2}\) vào, ta có:
\(B=5.\left(-\frac{1}{5}\right)^2-4.\left(-\frac{1}{2}\right)=\frac{11}{5}\)
c) \(C=6xy\left(xy-y^2\right)-8x^2\left(x-y^2\right)-5y^2\left(x^2-xy\right)\)
\(C=6x^2y^2-6xy^3-8x^3+8x^2y^2-5x^2y^2+5xy^3\)
\(C=9x^2y^2-xy^3-8x^3\)
Thay \(x=\frac{1}{2};y=2\) vào, ta có:
\(C=9.\left(\frac{1}{2}\right)^2.2^2-\frac{1}{2}.2^3-8.\left(\frac{1}{2}\right)^3=4\)
d) \(D=\left(3x+5\right)\left(2x-1\right)+\left(4x-1\right)\left(3x+2\right)\)
\(D=6x^2-3x+10x-5+12x^2+8x-3x-2\)
\(D=18x^2+12x-7\)
Ta có: \(\left|2\right|=\orbr{\begin{cases}x=-2\\x=2\end{cases}}\)
+) Với x = -2
\(D=18.\left(-2\right)^2+12.\left(-2\right)-7=41\)
+) Với x = 2
\(D=18.2^2+12.2-7=89\)
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a) 5x2 ( 3x2 -7x+2)-15x(x-3)
=15x4-35x3+10x2-15x2+45x
=15x4-35x3-5x2+45x
c) (x+3)(x-3)(x-2)(x+1)
=(x2-9)(x2+x-2x-2)
=(x2-9)(x2-x-2)
=x4-x3-2x2-9x2+9x+18
=x4-x3-11x2+9x+18
d)(2x+1)2+(4x-1)2+2(2x+1)(4x+1)
=2x2+4x+1-16x2-8x+1
=2x2+4x+1-16x2-8x+1+16x2-4x+8x-2
=2x2+7
e) (2x2-3x)(5x2-2x+1)-10x2(x+3)
=10x4 -4x3+2x2-15x3+6x2-3 -10x2-30x
=10x4-19x3-2x2-30x-3
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a) \(2x\left(5-3x^2\right)-10\left(6+x\right)\)
\(=10x-6x^3-60-10x\)
\(=\) \(-6x^3-60\)
a) \(2x\left(5-3x^2\right)-10\left(6+x\right)\\ =2x.5-2x.3x^2-10.6-10.x\\ =10x-6x^3-60-10x\)
b) \(3\left(-x+2\right)-6\left(1-x+5x^{20}\right)\\ =-3.x+3.2-6.1+6.x-5.5x^{20}\\ =-3x+6-6+6x-25x^{20}=25x^{20}+3x\)
c) \(7x\left(2-5x^2+\dfrac{1}{2}x^3\right)-14x\left(1-2x^2\right)\\ =7x.2-7x.5x^2+7x.\dfrac{1}{2}x^3-14x.1+14x.2x^2\\ =14x-25x^3+\dfrac{7}{2}x^4-14x+28x^3=3x^2+\dfrac{7}{2}x^4\)
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\(4.\left(3x+y\right)^2+\left(x+y\right)^2\)
\(=3x^2+6xy+y^2+x^2-2xy+y^2\)
\(=9x^2+6xy+y^2+x^2-2xy+y^2\)
\(=10x^2-4xy+2y^2\)
\(7.\left(x-4\right)^2+\left(x+4y\right)\)
\(=x^2-8x+16+x+4y\)
\(=x^2-7x+16+4y\)
\(10.\left(2x+7\right)^2+\left(-2x-3\right)^2\)
\(=4x^2+28x+49+4x^2+12x+9\)
\(=8x^2+40x+58\)
\(12.-\left(x+1\right)^2-\left(x-1\right)^2\)
\(=-\left(x^2+2x+1\right)-\left(x^2-2x+1\right)\)
\(=-x^2-2x-1+x^2+2x-1\)
\(=4x\)
\(5.-\left(x+5\right)^2-\left(x-3\right)^2\)
\(=-\left(x^2+10x+25\right)-\left(x^2-6x+9\right)\)
\(=-x^2-10-25+x^2+6x-9\)
\(=-16x-16\)
\(8.-\left(-2x+3\right)^2-\left(5x-3\right)^2\)
\(=4x^2+12x+9-25x^2+30x-9\)
\(=-21x^2+42x\)
\(11.-\left(2x-y\right)^2-\left(x+3y\right)^2\)
\(=-4x^2+4xy-y^2-\left(x^2+6xy+9y^2\right)\)
\(=-4x^2+4xy-y^2-x^2-6xy-9y^2\)
\(=-5x^2-2xy-10y^2\)
4: =9x^2+6xy+y^2+x^2-2xy+y^2
=10x^2+4xy+2y^2
5: =-x^2-10x-25-x^2+6x-9
=-4x-34
7; \(=x^2-8xy+16y^2+x+4y\)
10: \(=4x^2+28x+49+4x^2+12x+9\)
=8x^2+40x+58
11: =-4x^2+4xy-y^2-x^2-6xy-9y^2
=-5x^2-2xy-10y^2
a) \(3x\left(x-3\right)-5x\left(x+7\right)\)
\(=3x^2-9x-5x^2-35x\)
\(=-2x^2-44x\)
b) \(\dfrac{1}{5}x\left(10x-15\right)-2x\left(x-5\right)-12\)
\(=2x^2-3x-2x^2+10x-12\)
\(=7x-12\)