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bạn tham khảo 1 số bài rồi tự làm nhé
a) 3x−3+5(1−x)
=3x−3+5−5x
=3x−5x+2
=x(3−5)+2
=−2x+2
=2(1−x)
b) 12a2−3ab+8ac−2bc
=3a(4a−b)+2c(4a−b)
=(4a−b)(3a+2c)
c) x2−25+y2−2xy
=x2−2xy+y2−25
=(x−y)2−52
=(x−y−5)(x−y+5)
\(1.mx+my+5x+5y\)
\(=m\left(x+y\right)+5\left(x+y\right)\)
\(=\left(m+5\right)\left(x+y\right)\)
\(2.\left(a+b\right)\left(a-b\right)-\left(a+b\right)\left(a^2-ab+b^2\right)\)
\(=\left(a+b\right)\left(a-b-a^2+ab-b^2\right)\)
\(x^2-y^2+4x+4\)
\(=\left(x+2\right)^2-y^2\)
\(=\left(x+2+y\right)\left(x+2-y\right)\)
\(4x^2-y^2+8\left(y-2\right)\)
\(=4x^2-\left(y^2-8y+16\right)\)
\(=4x^2-\left(y-4\right)^2\)
\(=\left(2x+y-4\right)\left(2x-y+4\right)\)
\(=a^2\left(1-b^2\right)+b\left(b-1\right)+a\left(b-1\right)..\)
\(=a^2\left(1-b\right)\left(1+b\right)-b\left(1-b\right)-a\left(1-b\right).\)
\(=\left(a^2+a^2b-b-a\right)\left(1-b\right)\)
\(=\left(ab+a+b\right)\left(a-1\right)\left(1-b\right)\)
\(a^2+b^2-a^2b^2+ab-a-b\)
\(=a^2\left(1-b^2\right)+b\left(b-1\right)+a\left(b-1\right)\)
\(=a^2\left(1-b\right)\left(1+b\right)-b\left(1-b\right)-a\left(1-b\right)\)
\(=\left(a^2+a^2b-b-a\right)\left(1-b\right)\)
\(=\left(ab+a+b\right)\left(a-1\right)\left(1-b\right)\)
\(a^3b-ab^3+a^2+2ab+b^2\)
\(=\left(a^3b-ab^3\right)+\left(a^2+2ab+b^2\right)\)
\(=ab\left(a^2-b^2\right)+\left(a+b\right)^2\)
\(=ab\left(a-b\right)\left(a+b\right)+\left(a+b\right)^2\)
\(=\left(a+b\right)\left[ab\left(a-b\right)+\left(a+b\right)\right]\)
\(=\left(a+b\right)\left(a^2b-ab^2+a+b\right)\)
a) Đặt a + b = x ; a - b = y. Khi đó:
\(\left(a+b\right)^3-\left(a-b\right)^3\)
\(\Leftrightarrow x^3-y^3\)
\(\Leftrightarrow\left[x-y\right]\left[x^2+xy+y^2\right]\)
Thế lại vào ta có:
\(\Leftrightarrow\left[\left(a+b\right)-\left(a-b\right)\right]\left[\left(a+b\right)^2+\left(a+b\right)\left(a-b\right)+\left(a-b\right)^2\right]\)
\(\Leftrightarrow\left[\left(a-a\right)+\left(b+b\right)\right]\left[\left(a^2+b^2+2ab\right)+\left(a^2-b^2\right)+\left(a^2+b^2-2ab\right)\right]\)
\(\Leftrightarrow2b\left[\left(a^2+a^2+a^2\right)+\left(b^2-b^2+b^2\right)+\left(2ab-2ab\right)\right]\)
\(\Leftrightarrow2b\left[3a^2+b^2\right]\)
Mik làm tuỳ theo mình piết thôi nhé
a) ( a + b )3- ( a - b )3= a3 + b3 - a3 - b3 = a3 - a3 + b3 - b3 = 0
b) tương tự như ở trên!!! Hơi khác một tí!!!
c) ( 6x - 1 )2 - ( 3x + 2 ) = ..........
\(\left(a+b\right)^3-\left(a-b\right)^3\)
\(=\left(a+b-a+b\right)\left(\left(a+b\right)^2+\left(a+b\right)\left(a-b\right)+\left(a-b\right)^2\right)\)
\(=2b\left(\left(a+b\right)^2+\left(a^2-b^2\right)+\left(a-b\right)^2\right)\)
\(\left(a+b\right)^3+\left(a-b\right)^3\)
\(=\left(a+b+a-b\right)\left(\left(a+b\right)^2-\left(a+b\right)\left(a-b\right)+\left(a-b\right)^2\right)\)
\(=2a\left(\left(a+b\right)^2-\left(a^2-b^2\right)+\left(a-b\right)^2\right)\)
a) (a+b)3 -(a-b)3 = a3 + 3a2b + 3ab2 +b3 - a3 + 3a2b - 3ab2 +b3
= 2a3 + 6a2b + 2b3
1) \(a\left(a-b\right)\left(a+b\right)-\left(a+b\right)\left(a^2-ab+b^2\right)\)
\(=\left(a+b\right)\left(a^2-ab-a^2+ab-b^2\right)\)
\(=\left(a+b\right)\left(-b^2\right)\)
2) \(\left(a-b\right)^2-\left(b-a\right)\left(a+b\right)\)
\(=\left(a-b\right)^2+\left(a-b\right)\left(a+b\right)\)
\(=\left(a-b\right)\left(a-b+a+b\right)\)
\(=2a\left(a-b\right)\)