Ta có :
\(A=3\left(x^2+y^2\right)-\left(x^3+y^3\right)+1\)
\(=3\left(x^2+y^2+2xy-2xy\right)-\left(x+y\right)\left(x^2+y^2-xy\right)+1\)
\(=3\left[\left(x+y\right)^2-2xy\right]-2\left[\left(x^2+y^2+2xy\right)-3xy\right]+1\)
\(=3\left(2^2-2xy\right)-2\left[\left(x+y\right)^2-3xy\right]+1\)
\(=12-6xy-2.\left(4-3xy\right)+1\)
\(=12-6xy-8+6xy+1\)
\(=5\)
Vậy ...
cho x+y =1 . tinh gia tri cua bieu thuc A=x^3+y^3+3xy
chox-y=1. tinh gia tri cua bieu thuc B=x^3-y^3-3xy
cho x+y=1 . tinh gia tri cua bieu thuc C=x^3+y^3+3xy(x^2+y^2)+6x^2*y^2(x+y)
1. cho x+y=7 va xy=8 gia tri cua bieu thuc x3+y3 = ?
2. gia tri lon nhat cua bieu thuc B= 1+3x-x2 la ?
1. cho x+y=7 va xy=8 gia tri cua bieu thuc x3+y3 = ?
2. gia tri lon nhat cua bieu thuc B= 1+3x-x2 la ?
Cho x+y=2, tinh gia tri cua bieu thuc:
M=3(x^2+y^2)-(x^3+y^3)+1
Bai 2:Cho a+b=5,tinh gia tri bieu thuc:
M=3a^2-2a+3b^2-2b+6ab+100
1. biết x2-2y2=xy,y\(\ne\)0,x+y\(\ne\)0. thì gia tri cua bieu thuc Q=\(\frac{x+y}{x-y}\)=
2.cho x\(\ne\)0,y\(\ne\)0 thoa man x+y=4 ;xy=2 .gia tri cua bieu thuc A=\(\frac{1}{x^3}+\frac{1}{y^3}\)la
3.gia tri cua bieu thuc A=\(\frac{81^8-1}{\left(3^4+1\right)\left(3^8+1\right)\left(3^{16}+1\right)}\)la
tim gia tri nho nhat cua bieu thuc x^3+y^3 voi x+y=3
CTR cac bieu thuc sau luon nhan gia tri am voi moi gtri cua bienn : - x^2 - y^2 + 2x+ 2y -3
giai chi tiet giup to may bai nay nha
1. Cho tam giac ABC co trung tuyen AM . Goi I la trung diem cua AM. Tia BI cat AC tai D, qua M ke duong song song voi BD cat CD tai E. Biet BD=18cm , khih do ID = ? cm
2. gia tri lon nhat cua bieu thuc Q= 5-x2+2x2-4y2-4y
3 . gia tri cua x thoa man (12x-5)(4x-1)+(3x-7)(1-16x)=81 , x=?
4. x+y=3 , gia tri cua bieu thuc Q = x2+2xy+y2-4x-4y+1=?
5 . a+b+c=0 va abc=-2 thi a3+b3+c3= ?
6. rut gon bieu thuc(a2+b2)2-4a2b2voi a2-b2=5 ta duoc ket qua ?
1.cho phan thuc P=\(\frac{5x-4y}{5x+4y}\)voi 25x2+16y2=50xy.khi do gia tri cua bieu thuc P=\(\frac{1+P^2}{1-P^2}\)la
2.gia tri lon nhat cua bieu thuc B=\(\frac{14}{\frac{x^2}{4}-3x+16}la\)
3.gia tri cua a de da thuc A=2x3+7x2+ax+3 chia het cho B=(x+1)2la a=?
