cho hinh binh hanh ABCD; O la gaio diem cua AC va BD.E va F lan luot la trung diem cua OB va OD
a)cmr AE//CF
b)K la giao diem cua AE va CD. cmr DK=1/2KC
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Xét :\(D=\left(3+1\right)\left(3^2+1\right)\left(3^4+1\right)\left(3^8+1\right)\)
\(=\left(3-1\right)\left(3+1\right)\left(3^2+1\right)\left(3^4+1\right)\left(3^8+1\right).\frac{1}{2}\)
\(=\left(3^2-1\right)\left(3^2+1\right)\left(3^4+1\right)\left(3^8+1\right).\frac{1}{2}\)
\(=\left(3^4-1\right)\left(3^4+1\right)\left(3^8+2\right).\frac{1}{2}\)
\(=\left(3^8-1\right)\left(3^8+1\right).\frac{1}{2}\)
\(=\left(3^{16}-1\right).\frac{1}{2}\)
Vì \(\frac{3^{16}-1}{2}< 3^{16}-1\)
nên D < C
Vậy D < C
\(2x^2-x-6=0\)
\(\Leftrightarrow2x^2-x=6\)
\(\Leftrightarrow2x^2-x1=6\)
\(\Leftrightarrow x.\left(2x-1\right)=6\)
\(\Leftrightarrow x.\left(x+1\right)=6\)
\(\Rightarrow x=2\)
Ta có :
\(A=x^4-2x^3+3x^2-4x+5\)
\(=\left(x^4-2x^3+x^2\right)+\left(2x^2-4x+2\right)+3\)
\(=\left(x^2-x\right)^2+\left(\sqrt{2}x-\sqrt{2}\right)^2+3\)
Vì \(\hept{\begin{cases}\left(x^2-x\right)^2\ge0\forall x\\\left(\sqrt{2}x-\sqrt{2}\right)^2\ge0\forall x\end{cases}}\)
\(\Rightarrow\left(x^2-x\right)^2+\left(\sqrt{2}x-\sqrt{2}\right)^2\ge0\forall x\)
\(\Rightarrow\left(x^2-x\right)^2+\left(\sqrt{2}x-\sqrt{2}\right)^2+3\ge3\forall x\)
Dấu bằng xảy ra khi vì chỉ khi \(\hept{\begin{cases}\left(x^2-x\right)^2=0\\\left(\sqrt{2}x-\sqrt{2}=0\right)\end{cases}\Leftrightarrow\hept{\begin{cases}x^2-x=0\\\sqrt{2}x-\sqrt{2}=0\end{cases}\Leftrightarrow\hept{\begin{cases}x\left(x-1\right)=0\\\sqrt{2}\left(x-1\right)\end{cases}}}}\)
\(\Leftrightarrow x=1\)
Vậy \(A_{min}=3\)tại \(x=1\)
x2-2xy-9z2+y2
= ( x2-2xy+y2 ) -9z2
=(x-y)2-(3z)2
=(x-y-3z)(x-y+z)
Thay x=6;y=-4;z=30 ta có:
(6+4-90)(6+4+90)
=(-80).100
=-8000
Hk tốt
a, a(x-y) + bx - by = a(x - y ) +b.(x-y) = (x-y)(a-b)
b, ac+bc + a + b = c.(a+b) +(a+b) = (a+b)(c+1)
c, \(5a^2-5ax-7a+7x=5a.\left(a-x\right)-7.\left(a-x\right)=\left(a-x\right)\left(5a-7\right)\)
d, \(7z^2-7yz-4z+4y=7z.\left(z-y\right)-4.\left(z-y\right)=\left(z-y\right)\left(7z-4\right)\)
e, \(x^3+3x^2+3x+9=x^2.\left(x+3\right)+3\left(x+3\right)=\left(x+3\right)\left(x^2+3\right)\)
g, \(pq-p^2-5\left(p-q\right)=p.\left(q-p\right)+5\left(q-p\right)=\left(q-p\right)\left(p+5\right)\)
ARMY (.) nha