tính :
\(A=\left(a+b+c\right)^3+\left(a-b\cdot c\right)^3-ba\left(b+c\right)^2\)
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26 tháng 11 2022
\(C=\dfrac{\left(b-c+c-a\right)^3+3\left(b-c\right)\left(c-a\right)\left(b-c+c-a\right)+\left(a-b\right)^3}{a^2b-a^2c+b^2c-b^2a+c^2a-c^2b}\)
\(=\dfrac{3\left(b-c\right)\left(c-a\right)\left(b-a\right)}{a^2b-b^2a-a^2c+b^2c+c^2a-c^2b}\)
\(=\dfrac{3\left(b-c\right)\left(c-a\right)\left(b-a\right)}{\left(a-b\right)\cdot ab-c\left(a-b\right)\left(a+b\right)+c^2\left(a-b\right)}\)
\(=\dfrac{3\left(b-c\right)\left(a-c\right)\left(a-b\right)}{\left(a-b\right)\left(ab-ac-bc+c^2\right)}\)
\(=\dfrac{3\left(b-c\right)\left(a-c\right)}{a\left(b-c\right)-c\left(b-c\right)}=3\)
PN
8 tháng 11 2015
a. Ta có:
\(a^2\left(b-c\right)+b^2\left(c-a\right)+c^2\left(a-b\right)=a^2\left(b-c\right)-b^2\left(b-c+a-b\right)+c^2\left(a-b\right)=a^2\left(b-c\right)-b^2\left(b-c\right)-b^2\left(a-b\right)+c^2\left(a-b\right)\)
\(=\left(a-b\right)\left(c-a\right)\left(c-b\right)\)
và \(ab^2-ac^2-b^3+bc^2=a\left(b^2-c^2\right)-b\left(b^2-c^2\right)=\left(a-b\right)\left(b-c\right)\left(b+c\right)\)
Vậy, \(A=\frac{\left(a-b\right)\left(c-a\right)\left(c-b\right)}{\left(a-b\right)\left(b-c\right)\left(b+c\right)}=\frac{c-a}{-c-b}=\frac{a-c}{c+b}\)
AT
24 tháng 8 2018
a/ \(A=\left(3+1\right)\left(3^2+1\right)\left(3^4+1\right)...\left(3^{64}+1\right)\)
\(2A=2\left(3+1\right)\left(3^2+1\right)\left(3^4+1\right)...\left(3^{64}+1\right)\)
\(2A=\left(3-1\right)\left(3+1\right)\left(3^2+1\right)\left(3^4+1\right)...\left(3^{64}+1\right)\)
\(2A=\left(3^2-1\right)\left(3^2+1\right)\left(3^4+1\right)...\left(3^{64}+1\right)\)
\(2A=\left(3^4-1\right)\left(3^4+1\right)...\left(3^{64}+1\right)\)
\(\Rightarrow2A=3^{128}-1\Rightarrow A=\dfrac{3^{128}-1}{2}\)
5 tháng 11 2019
\(x^3-y^3-36xy\)
\(=\left(x-y\right)^3+3xy\left(x-y\right)-36xy\)
\(=12^3+36xy-36xy\)
\(=1728\)
LM
8 tháng 9 2016
\(\left(a+b+c\right)^3=\left[\left(a+b\right)+c\right]^3=\left(a+b\right)^3+3\left(a+b\right)^2c+3\left(a+b\right)c^2+c^3\)
\(=\left(a^3+3a^2b+3b^2a+b^3\right)+3c\left(a^2+2ab+b^2\right)+3c^2\left(a+b\right)+c^3\)
\(=a^3+3a^2b+3b^2a+b^3+3a^2c+6abc+3b^2c+3ac^2+3bc^2+c^3\)
\(=a^3+b^3+c^3+\left(3a^2b+3b^2a+3b^2c+3c^2b+3a^2c+3c^2a+6abc\right)\)
\(=a^3+b^3+c^3+3\left(a^2b+b^2a+b^2c+c^2b+a^2c+c^2a+2abc\right)\)
\(=a^3+b^3+c^3+3\left(a+b\right)\left(b+c\right)\left(c+a\right)\)
\(A=\left(\left(a+b\right)+c\right)^3+\left(\left(a-b\right)-c\right)^3-ba\left(b+c\right)^2\\ \)
\(A=\left(a+b\right)^3+3\left(a+b\right)^2c+3\left(a+b\right)c^2+c^3\)\(-\left(a-b\right)^3-3\left(a-b\right)^2c+3\left(a-b\right)c^2-c^3\)\(-ba\left(b^2+2bc+c^2\right)\)
\(A=a^3+3a^2b+3ab^2+b^3+3\left(a^2+2ab+b^2\right)c+3ac^2+3bc^2+c^3\)\(-\left(a^3-3a^2b+3ab^2-b^3\right)-3\left(a^2-2ab+b^2\right)c\)\(+3ac^2-3bc^2-c^3-b^3a-2ab^2c-bac^2\)
\(A=a^3+3a^2b+3ab^2+b^3+3a^2c+6abc+3b^2c\)\(+3ac^2+3bc^2+c^3-a^3+3a^2b-3ab^2+b^3\)\(-3a^2c+6abc-ab^2c+3ac^2-3bc^2-c^3-b^3a\)\(-2ab^2c-bac^2\)
\(A=6a^2b+2b^3+12abc+3b^2c-3ab^2c-c^3-b^3a-bac^2\)
ko bt có đúng ko nữa
nếu sai cho mình xin lỗi nha