Ta có : A=2²+2⁴+2⁶+...+2²⁰

=(2²+2⁴)+(2⁶+2⁸)+...+(2¹⁸+2²⁰)

=2²(1+2²)+2⁶(1+2²)+...+2¹⁸(1+2²)

=2².5+2⁶.5+...+2¹⁸.5 chia hết cho 5

Vậy A chia hết cho 5.

\(A=2^2+2^4+2^6..+2^{18}+2^{20}\)

\(\Leftrightarrow A=\left(2^2+2^4\right)+\left(2^6+2^8\right)+...+\left(2^{18}+2^{20}\right)\)

\(\Leftrightarrow A=20+2^4.\left(2^2+2^4\right)+...+2^{16}.\left(2^2+2^4\right)\)

\(\Leftrightarrow A=20+2^4.20+..+2^{16}.20\)

\(\Leftrightarrow A=20\left(1+2^4+..+2^{16}\right)\)

Vì \(20⋮5\)

\(\Rightarrow A=20\left(1+2^4+..+2^{16}\right)⋮5\)

Vậy \(A⋮5\)

hok tốt!!

\(A=2^2+2^4+2^6+2^8+....+2^{18}+2^{20}\)

\(A=\left(2^2+2^4\right)+\left(2^6+2^8\right)+....+\left(2^{18}+2^{20}\right)\)

\(A=2^2\left(1+2^2\right)+2^6\left(1+2^2\right)+....+2^{18}\left(1+2^2\right)\)

\(A=2^2\cdot5+2^6\cdot5+...+2^{18}\cdot5\)

\(A=5\left(2^2+2^6+...+2^{18}\right)\)

=> A chia hết cho 5

A=1+2+2²+...+2²⁰⁰⁹ gồm 2010 số
A=(1+2+2²)+(2³+2⁴+2⁵)+...+(2²⁰⁰⁷+2²⁰⁰⁸+2²⁰⁰⁹⁾
A=7.1+7.2³+...+7.2²⁰⁰⁷(. là dấu nhân nhaaa)
A=7.(1+2³+...+2²⁰⁰⁷)⋮7
Vậy A⋮7
tích đúng hộ mikkkkk

 

Tọa độ giao điểm A,B là nghiệm của hệ phương trình:

\(\left\{{}\begin{matrix}x^2=2x+3\\y=2x+3\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}\left(x-3\right)\left(x+1\right)=0\\y=2x+3\end{matrix}\right.\Leftrightarrow\left(x,y\right)\in\left\{\left(3;9\right);\left(-1;1\right)\right\}\)

vậy: A(3;9); B(-1;1)

a) \(\left\{{}\begin{matrix}\left(m-1\right)x+y=2\\mx+y=m+1\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}\left(m-1\right)x+y=2\\\left(m-1\right)-mx=2-\left(m+1\right)\end{matrix}\right.\)\(\Leftrightarrow\left\{{}\begin{matrix}\left(m-1\right)x+y=2\\-x=1-m\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}\left(m-1\right)^2+y=2\\x=m-1\end{matrix}\right.\)\(\Leftrightarrow\left\{{}\begin{matrix}y=2-\left(m-1\right)^2\\x=m-1\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}y=-m^2+2m+1\\x=m-1\end{matrix}\right.\)

\(2x+y=2\left(m-1\right)+\left(-m^2+2m+1\right)=2m-2-m^2+2m+1=-m^2+4m-1=-\left(m^2-4m+4\right)+3=-\left(m-2\right)^2+3\le3\)

Dấu "=" xảy ra \(\Leftrightarrow m=2\)

\(a,HPT\Leftrightarrow\left\{{}\begin{matrix}mx-x+y=2\\mx+y=m+1\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}mx+y=x+2\\mx+y=m+1\end{matrix}\right.\\ \Leftrightarrow x+2=m+1\Leftrightarrow x=m-1\\ \Leftrightarrow\left(m-1\right)^2+y=2\\ \Leftrightarrow y=2-\left(m-1\right)^2\)

\(2x+y\le3\\ \Leftrightarrow2m-2+2-m^2+2m-1-3\le0\\ \Leftrightarrow-m^2+4m-4\le0\\ \Leftrightarrow-\left(m-2\right)^2\le0\left(luôn.đúng\right)\)

Vậy ta được đpcm

b, \(x+y=-4\Leftrightarrow x=-4-y\Leftrightarrow\left\{{}\begin{matrix}m-1=-4-y\left(1\right)\\y=2-\left(m-1\right)^2\left(2\right)\end{matrix}\right.\)

Thế (2) vào (1)

\(\Leftrightarrow m-1=-4-2+\left(m-1\right)^2\\ \Leftrightarrow m-1=-6+m^2-2m+1\\ \Leftrightarrow m^2-3m-4=0\\ \Leftrightarrow\left[{}\begin{matrix}m=-1\\m=4\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}y=2-4=-2\\y=2-9=-7\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=-2\\x=3\end{matrix}\right.\)

Vậy \(\left(x;y\right)=\left\{\left(-2;-2\right);\left(3;-7\right)\right\}\)

Tham khảo:

When a tropical storm reaches 120 kilometers per hour, it is called a typhoon

Wearing uniforms encourages students to be proud of being students of their school

the weather was snowy, we couldn't go to work yesterday
put the garbage into the dustbins, we will minimize pollution
so slowly that his students get bored
difficult to find a better solution

When a tropical storm reaches 120 kilometers per hour, it is called a typhoon

Wearing uniforms encourages students to be proud of being students of their school

the weather was snowy, we couldn't go to work yesterday
put the garbage into the dustbins, we will minimize pollution
so slowly that his students get bored
difficult to find a better solution

17 surprisingly

18 time-consuming

19 replacing

20 independent

21 qualifications

22 activists