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Ta có: \(89^6=496981290916\) = 4969**290961
\(\Rightarrow\) Số tương ứng với ** là 81
Vậy ** = 81 thì \(89^6\) = 4969**290961
\(a,\left(x+1\right)^2-\left(x-1\right)^2-3\left(x+1\right)\left(x-1\right)\)
\(=x^2+2x+1-\left(x^2-2x+1\right)-3\left(x^2-1\right)\)
\(=x^2+2x+1-x^2+2x-1-3x^2+2=-3x^2+4x+2\)\(b,5\left(x+2\right)\left(x-2\right)-\left(2x-3\right)^2-x^2+17\)
\(=5\left(x^2-4\right)-\left(4x^2-12x+9\right)-x^2+17\)
\(=5x^2-20-4x^2+12x-9-x^2+17=12x-12\)
. Giúp nha
\(9\left(x-y\right)^2-4\left(x+y\right)^2=\left[3\left(x-y\right)-2\left(x+y\right)\right]\left[3\left(x-y\right)+2\left(x+y\right)\right]\)
\(=\left(3x-3y-2x-2y\right)\left(3x-3y+2x+2y\right)\)
\(=\left(x-5y\right)\left(5x-y\right)\)
\(x^4+2014x^2+2013x+2014\)
\(=x^4+2014x^2+2014x-x+2014\)
\(=\left(x^4-x\right)+\left(2014x^2+2014x+2014\right)\)
\(=x\left(x^3-1\right)+2014\left(x^2+x+1\right)\)
\(=x\left(x-1\right)\left(x^2+x+1\right)+2014\left(x^2+x+1\right)\)
\(=\left(x^2+x+1\right)\left(x^2-x+2014\right)\)
b)\(x^8+7x^4+6\)
\(=x^8+x^4+6x^4+6\)
\(=x^4\left(x^4+1\right)+6\left(x^4+1\right)\)
\(=\left(x^4+1\right)\left(x^4+6\right)\)
b) \(x^8+7x^4+16\)
\(=\left(x^8+8x^4+16\right)-x^4\)
\(=\left[\left(x^4\right)^2+2.x^4.4+4^2\right]-x^4\)
\(=\left(x^4+4\right)^2-\left(x^2\right)^2\)
\(=\left(x^4+4-x^2\right)\left(x^4+4+x^2\right)\)
Ta có \(a^2+b^2\ge\dfrac{\left(a+b\right)^2}{2}\).
Suy ra \(x^4+y^4\ge\dfrac{\left(x^2+y^2\right)^2}{2}\)\(\ge\dfrac{\left[\dfrac{\left(x+y\right)^2}{2}\right]^2}{2}=\dfrac{\left(x+y\right)^4}{8}\). (đpcm).
\(x^2-3x+1\)
\(=x^2-2.x.\frac{3}{2}+\frac{9}{4}-\frac{5}{4}\)
\(=\left(x-\frac{3}{2}\right)^2-\frac{5}{4}\)
\(=\left(x-\frac{3}{2}-\frac{\sqrt{5}}{2}\right)\left(x-\frac{3}{2}+\frac{\sqrt{5}}{2}\right)\)
Đặt
\(A=x^4-4x^3+8x+3\)
Giả sử
\(A=\left(x^2+ax+b\right)\left(x^2+cx+d\right)\)
\(=x^4+cx^3+dx^2+ax^3+acx^2+adx+bx^2+bcx+bd\)
\(=x^4+\left(a+c\right)x^3+\left(b+ac+d\right)x^2+\left(ad+bc\right)x+bd\)
\(\left[\begin{array}{nghiempt}a+c=-4\\b+ac+d=0\\ad+bc=8\\bd=3\end{array}\right.\)
\(\left[\begin{array}{nghiempt}a=-2\\b=-3\\c=-2\\d=-1\end{array}\right.\)
\(A=\left(x^2-2x-3\right)\left(x^2-2x-1\right)\)
dài dòng
\(x^4-4x^3+8x+3=x^4-2x^3-2x^3-x^2+4x^2-3x^2+2x+6x+3\)
\(=\left(x^4-2x^3-x^2\right)-\left(2x^3-4x^2-2x\right)-\left(3x^2-6x-3\right)\)
\(=x^2\left(x^2-2x-1\right)-2x\left(x^2-2x-1\right)-3\left(x^2-2x-1\right)\)
\(=\left(x^2-2x-1\right)\left(x^2-2x-3\right)\)