rút gọn biểu thức
5x+3-|6x-4|
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1/2 x 2 (6x – 3) – x( x 2 + 1/2) + 1/2.(x + 4)
= (3 x 3 – 3/2. x 2 ) – ( x 3 + 1/2.x) + (1/2.x + 2)
= 3 x 3 - 3/2 x 2 – x 3 - 1/2 x + 1/2 x + 2
= ( 3 x 3 – x 3 ) - 3/2. x 2 – (1/2 x - 1/2 x) + 2
= 2 x 3 - 3/2 x 2 + 2
Ta có
M = ( 2 x + 3 ) ( 4 x 2 – 6 x + 9 ) – 4 ( 2 x 3 – 3 ) = ( 2 x + 3 ) [ ( 2 x ) 2 – 2 x . 3 + 3 2 ] – 8 x 3 + 12 = ( 2 x ) 3 - 3 3 – 8 x 3 + 12 = 8 x 3 + 27 – 8 x 3 + 12 = 39
Vậy giá trị của M là một số lẻ
Đáp án cần chọn là: A
a,ĐKXĐ:\(\left\{{}\begin{matrix}x-4\ne0\\x+4\ne0\\x^2-16\ne0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x\ne4\\x\ne-4\\x\ne\pm4\end{matrix}\right.\Leftrightarrow x\ne\pm4\)
b,\(\dfrac{4}{x-4}+\dfrac{3}{x+4}.\dfrac{6x}{x^2-16}=\dfrac{4}{x-4}+\dfrac{18x}{\left(x-4\right)\left(x+4\right)^2}=\dfrac{4\left(x+4\right)^2+18x}{\left(x-4\right)\left(x+4\right)^2}=\dfrac{4\left(x^2+8x+16\right)+18x}{\left(x-4\right)\left(x+4\right)^2}=\dfrac{4x^2+32x+64+18x}{\left(x-4\right)\left(x+4\right)^2}=\dfrac{4x^2+50x+64}{\left(x-4\right)\left(x+4\right)^2}\)
\(\left(6x+1\right)^2+\left(6x-1\right)^2-2\left(1+6x\right)\left(6x-1\right)\)
\(=\left(6x+1-6x+1\right)^2\)
\(=2^2=4\)
\(3\left(2^2+1\right)\left(2^4+1\right)\left(2^8+1\right)\left(2^{16}+1\right)\)
\(=\left(2^2-1\right)\left(2^2+1\right)\left(2^4+1\right)\left(2^8+1\right)\left(2^{16}+1\right)\)
\(=\left(2^4-1\right)\left(2^4+1\right)\left(2^8+1\right)\left(2^{16}+1\right)\)
\(=\left(2^8-1\right)\left(2^8+1\right)\left(2^{16}+1\right)\)
\(=\left(2^{16}-1\right)\left(2^{16}+1\right)\)
\(=2^{32}-1\)
a) \(\left(6x+1\right)^2+\left(6x-1\right)^2-2\left(1+6x\right)\left(6x-1\right)\)
\(=\left(6x+1\right)\left(6x+1\right)+\left(6x-1\right)\left(6x-1\right)-2\left(1+6x\right)\left(6x-1\right)\)
\(=\left(6x+1\right)\left(6x+1\right)+\left(6x-1\right)\left[\left(6x-1\right)-2\left(1+6x\right)\right]\)
\(=\left(6x+1\right)\left(6x+1\right)+\left(6x-1\right)\left(6x-1-2-12x\right)\)
\(=36x^2+12x+1+\left(6x-1\right)\left(-6x-3\right)\)
\(=36x^2+12x+1+\left(-36x^2-12x+3\right)\)
\(=36x^2+12x+1-36x^2-12x+3\)
\(=4\)
\(a,=a^3+3a^2b+3ab^2+b^3-a^3+3a^2b-3ab^2+b^3-2b^3=6a^2b\\ b,=\left(6x+1-6x+1\right)^2=2^2=4\)
5x+3-|6x-4|
=5x+3-(6x-4)
=5x+3-6x+4
=(5x-6x)+(3+4)
=x+7
\(5x+3-|6x-4|\)
\(=5x+3-6x-4\)
\(=\left(5x-6x\right)+\left(3+4\right)\)
\(=x+7\)