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B:6 so sánh
a, \(7^{18}\) + \(7^{19}\) và \(7^{20}\)
ta có : \(7^{18}\) + \(7^{19}\) = \(7^{37}\)
mà \(7^{37}\) > \(7^{12}\)
\(\Rightarrow\) \(7^{18}\) + \(7^{19}\) > \(7^{20}\)
Câu 2:
25.20,04 + 75.20, 04 - 2004.20,03 + 2004.20,04
= 20,04(25 + 75 - 2003 + 2004)
= 20,04.101 = 2024,04
C3: A=\(\frac{2}{3\cdot5}+\frac{2}{5\cdot7}+\frac{2}{7\cdot9}+...+\frac{2}{2011\cdot2013}+\frac{2}{2013\cdot2015}\)
\(=\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+...+\frac{1}{2013}-\frac{1}{2015}\)
\(=\left(\frac{1}{3}-\frac{1}{2015}\right)+\left(\frac{1}{5}-\frac{1}{5}\right)+\left(\frac{1}{7}-\frac{1}{7}\right)+...+\left(\frac{1}{2013}-\frac{1}{2013}\right)\)
\(=\left(\frac{2015}{6045}-\frac{3}{6045}\right)+0+...+0=\frac{2012}{6045}\)
mấy câu kia mình lười làm lắm bạn
Chúc bạn học tốt!^_^
- Viết gọn các tổng , hiệu , tích sau bang cách dùng lũy thừa
a ) xxx + aaaa
=x3+a4
b ) aaa - bb
=a3-b2
- Tìm các số tự nhiên x biết:
*x2=16
=>x2=42
=>x=4
*(x+1)2=9
=>(x+1)2=32
=>x+1=3
=>x+1=3
=>x=3-1
=>x=2
*x3=27
=>x3=33
=>x=3
*3x+1=27
=>3x+1=33
=>x+1=3
=>x=3-1
=>x=2
*2x=36
=>2x=25
=>x=5
a)
- \(A=2+2^2+2^3+...+2^{60}\)
\(=\left(2+2^2\right)+\left(2^3+2^4\right)+...+\left(2^{59}+2^{60}\right)\)
\(=2\left(1+2\right)+2^3\left(1+2\right)+...+2^{59}\left(1+2\right)\)
\(=2.3+2^3.3+...+2^{59}.3\)
\(=3\left(2+2^3+...+2^{59}\right)⋮3\)
- \(A=2+2^2+2^3+...+2^{60}\)
\(=\left(2+2^2+2^3\right)+\left(2^4+2^5+2^6\right)+...+\left(2^{58}+2^{59}+2^{60}\right)\)
\(=2\left(1+2+2^2\right)+2^4\left(1+2+2^2\right)+...+2^{58}\left(1+2+2^2\right)\)
\(=2.7+2^4.7+...+2^{58}.7\)
\(=7\left(2+2^4+2^{58}\right)⋮7\)
- \(A=2+2^2+2^3+...+2^{60}\)
\(=\left(2+2^2+2^3+2^4\right)+\left(2^5+2^6+2^7+2^8\right)+...+\left(2^{57}+2^{58}+2^{59}+2^{60}\right)\)
\(=2\left(1+2+2^2+2^3\right)+2^5\left(1+2+2^2+2^3\right)+...+2^{57}\left(1+2+2^2+2^3\right)\)
\(=2.15+2^5.15+...+2^{57}.15\)
\(=15\left(2+2^5+2^{57}\right)⋮15\)
b) \(B=1+5+5^2+5^3+...+5^{96}+5^{97}+5^{98}\)
\(=\left(1+5+5^2\right)+\left(5^3+5^4+5^5\right)+...+\left(5^{96}+5^{97}+5^{98}\right)\)
\(=\left(1+5+5^2\right)+5^3\left(1+5+5^2\right)+..+5^{96}\left(1+5+5^2\right)\)
\(=31+5^3.31+...+5^{96}.31\)
\(=31\left(1+5^3+...+5^{96}\right)⋮31\)
a) \(\left(x-1\right):3=2^3\) \(\Leftrightarrow\) \(\left(x-1\right):3=8\) \(x+1=24\) \(\Leftrightarrow\) \(x=23\) vậy \(x=23\)
b) \(12-2\left(x+5\right)=-10\) \(\Leftrightarrow\) \(12-2x-10=-10\)
\(\Leftrightarrow\) \(-2x=-12\) \(\Leftrightarrow\) \(x=6\) vậy \(x=6\)
c) \(x-12\left(x+5\right)=-10\) \(\Leftrightarrow\) \(x-12x-60=-10\)
\(\Leftrightarrow\) \(-11x=50\) \(\Leftrightarrow\) \(x=\dfrac{50}{-11}\) vậy \(x=\dfrac{50}{-11}\)
e) \(13-x:2=10\Leftrightarrow-x:2=-3\Leftrightarrow x=\dfrac{3}{2}\)
f) \(\left|12-x\right|-7=5\)
th1 : \(x\le12\) thì \(\left|12-x\right|-7=5\) \(\Leftrightarrow\) \(12-x-7=5\) \(\Leftrightarrow\) \(-x=0\Leftrightarrow x=0\)
th2 : \(x>12\) thì \(\left|12-x\right|-7=5\) \(\Leftrightarrow\) \(x-12-7=5\) \(\Leftrightarrow\) \(x=24\) vậy \(x=0;x=24\)
i) \(x^2-7=2\Leftrightarrow x^2=9\Leftrightarrow x=3\) vậy \(x=3\)
k) \(x^3-4=-12\) \(\Leftrightarrow\) \(x^3=-8\) \(\Leftrightarrow x=-2\) vậy \(x=-2\)
a)\(\left(x-1\right):3=2^3\Rightarrow x-1=2^3.3=24\Rightarrow x=25\)
b)\(12-2\left(x+5\right)=-10\Leftrightarrow12-2x-10=-10\Rightarrow2-2x=-10\Rightarrow2x=12\Rightarrow x=6\)c)\(x-12\left(x+5\right)=-10\Rightarrow x-12x-60=-10\Rightarrow-11x-60=-10\Rightarrow-11x=-70\Rightarrow x=\dfrac{70}{-11}\)d)\(6-\left|x\right|=5\Rightarrow\left|x\right|=1\Rightarrow x=\left\{\pm1\right\}\)
Làm nốt nha
Đề mk ko hiểu gì cả
sao ko hiểu