Ch
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biet:a+b=2,a×b=-1 tinh:
Cho biet:a+b=2,a×b=-1 tinh:
a, a binh+b binh
b,a mu ba+b mu ba
cac ban oi giup minh voi
1.tim a,b thuoc Z,biet:a.(2b-3)=-6
2.cho x,y thuoc Z thoa man x mu 2 +y mu 2 chia het cho 3.chung to x va y chia het cho 3.
tim x nguyen biet:
a 8.(x mu 2 +3).(5-x)
b)(2x + 1)mu 2=25
c) (1-3x)mu3 =64
d)(4-x)mu3 =-27
e) xmu2 -5x =0
b: \(\left(2x+1\right)^2=25\)
=>\(\left[{}\begin{matrix}2x+1=5\\2x+1=-5\end{matrix}\right.\)
=>\(\left[{}\begin{matrix}2x=4\\2x=-6\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=2\\x=-3\end{matrix}\right.\)
c: \(\left(1-3x\right)^3=64\)
=>\(\left(1-3x\right)^3=4^3\)
=>1-3x=4
=>3x=1-4=-3
=>x=-3/3=-1
d: \(\left(4-x\right)^3=-27\)
=>\(\left(4-x\right)^3=\left(-3\right)^3\)
=>4-x=-3
=>x=4+3=7
e: \(x^2-5x=0\)
=>\(x\left(x-5\right)=0\)
=>\(\left[{}\begin{matrix}x=0\\x-5=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=0\\x=5\end{matrix}\right.\)
tim ba so a;b;c biet:a+b-c=-3;a-b+c=11;a-b-c=-1
cho a+b+c=0 va a binh phuong+ b binh phuong+ c binh phuing=1 .tinh m=a mu 4 + b mu 4 + c mu 4
cậu dùng bất đẳng thức bunhia cópki cho e bộ số là (x2,y2,z2)và (1,1,1) là được
CÓ gì ko hiểu hỏi riêng mình nha
cho a+b+c=0;a binh+b binh+c binh=1.
Tinh M=a mu4+b mu4+c mu 4
ta có a+b+c=0=>(a+b+c)^2=0
=>a^2+b^2+c^2+2ab+2ac+2bc=0
=>1+2(ab+bc+ac)=0(vì a^2+b^2+c^2=1)
=>ab+bc+cd=-1/2
=>(ab+bc+cd)^2=1/4
=>a^2b^2+a^2c^2+b^2c^2+2a^2bc+2ab^2c+2abc^2=1/4
=>a^2b^2+a^2c^2+b^2c^2+2abc(a+b+c)=1/4
=>a^2b^2 +a^2c^2+b^2c^2=1/4(vì a+b+c=0)*
mặt khác a^2+b^2+c^2=1
=>(a^2+b^2+c^2)^2=1
=>a^4+b^4+c^4+2a^2b^2+2a^2c^2+2b^2c^2=1
=>a^4+b^4+c^4+2(a^2b^2+a^2c^2+b^2c^2)=1
=>a^4+b^4+c^4+2.1/4=1(theo *)
=>a^4+b^4+c^4=1- 1/2=1/2(dpcm)
tim 2 so a va b biet:a-b=0,9va a nhân 6-b=6,4
cho cac da thuc
A=x mu 2-2x-y+3y-1
B= -2x mu 2+3y mu 2-5x+y+3
a)Tinh: A+B ; A-B
b)Tinh gia tri cua da thuc A tai x=1;y =-2
\(A=x^2-2x-y+3y-1\)
\(B=-2x^2+3y^2-5x+y+3\)
a) \(A+B=\left(x^2-2x-y+3y-1\right)+\left(-2x^2+3y^2-5x+y+3\right)\)
\(=x^2-2x-y+3y-1-2x^2+3y^2-5x+y+3\)
\(=\left(x^2-2x^2\right)+3y^2+\left(-2x-5x\right)+\left(-y+3y+y\right)+3-1\)
\(=-x^2+3y^2-7x+3y+2\)
\(A-B=\left(x^2-2x-y+3y-1\right)-\left(-2x^2+3y^2-5x+y+3\right)\)
\(=x^2-2x-y+3y-1+2x^2-3y^2+5x-y-3\)
\(=\left(x^2+2x^2\right)-3y^2+\left(-2x+5x\right)+\left(-y+3y-y\right)-1-3\)
\(=3x^2-3y+3x+y-4\)
b) tại x=1 ; x=-2 ta có:
\(A=1^2-2.1-\left(-2\right)+3.\left(-2\right)-1\)
\(A=1-2+2-6-1=-6\)
Vậy -6 là giá trị của đa thức A tại x=1 y=-2
a) \(A+B=\left(x^2-2x-y+3y-1\right)+\left(-2x^2+3y^2-5x+y+3\right)\)
\(=-x^2+3y^2-7x+3y+2\)
\(A-B=\left(x^2-2x-y+3y-1\right)-\left(-2x^2+3y^2-5x+y+3\right)\)
\(=3x^2-3y^2+3x+2y-4\)
b) \(A\left(1;-2\right)=1^2-2\cdot1-\left(-2\right)+3\cdot\left(-2\right)-1\)
\(=1-2+2-6-1\)
\(=-6\)
bai 4 , tinh gia tri bieu thuc ;
a,A=2 mu 1 + 2 mu 2 +2 mu 3 +......+2 mu 2019
b, B=1+3+3 mu 2 +3 mu 3 +......+3 mu 2020
\(a,A=2^1+2^2+2^3+...+2^{2019}\)
\(2A=2^2+2^3+2^4+...+2^{2020}\)
\(\Rightarrow2A-A=A=2^{2020}-2\)
\(B=1+3+3^2+3^3+...+3^{2020}\)
\(3B=3+3^2+3^3+...+3^{2021}\)
\(3B-B=2B=3^{2021}-1\)
\(B=\frac{3^{2021}-1}{2}\)
a,\(A=2^1+2^2+2^3+...+2^{2019}\)
\(2A=2^2+2^3+2^4+...+2^{2020}\)
\(2A-A=\left[2^2+2^3+2^4+...+2^{2020}\right]-\left[2^1+2^2+...+2^{2019}\right]\)
\(A=2^{2020}-2^1=2^{2020}-2\)
b, \(B=1+3+3^2+3^3+...+3^{2020}\)
\(3B=3+3^2+3^3+...+3^{2021}\)
\(3B-B=\left[3+3^2+3^3+...+3^{2021}\right]-\left[1+3+3^2+...+3^{2020}\right]\)
\(2B=3^{2021}-1\)
\(B=\frac{3^{2021}-1}{2}\)
a,Đặt A=2+22+23+...+22019
2A=2(2+22+23+...+22019)
2A=22+23+24+...+22020
2A-A=22+23+24+...+22020-2-22-23-...-22019
A=22020-2
Câu b thì nhân 3 lên rồi lấy 3B-B thi sẽ được 2B sau đó chia cho 2 là đượckết quả \(\frac{3^{2021}-3}{2}\)
1)CMR:(a+b-c)+(a-b)-(a-b-c)=a+b
2)chung minh A va B la hai so doi nhau biet:A=a-b+c;B=-a+b-c
3)cho a-b=1.tinhS biet :
S=-(a-b-c)+(-c+b+a)-(a+b)
ai lam duov 5 tick luon