已知x=√3+√2,y=√3-√2,求代数式3x²-5xy+3y²的值要过程

显示全部楼层 · 2012-12-23 19:56:37

见图...

千问 · 2012-12-23 19:56:37

3x^2-5xy+3y^2=3(x+y)^2-6xy-5xy=3(x+y)^2-11xyx+y=2根号3
xy=3-2=1代入得：原式=3*(2根号3)^2-11=3*4*3-11=36-11=25...

千问 · 2012-12-23 19:56:37

3x2-5xy+3y2=3x2-6xy+3y2+xy=3(x2-2xy+y2)+xy=3(x-y)2+xy=3[√3+√2-(√3-√2)]^2+(√3+√2)(√3-√2)=3[√3+√2-√3+√2]^2+1=3(2√2)^2+1=3*8+1=24+1...

千问 · 2012-12-23 19:56:37

3x2-5xy+3y2=3 x2+3y2+6xy-11 xy=3(x2+y2+2xy)-11xy=3(x+y)^2-11xy=3(√3+√2+√3-√2)^2-11(√3+√2)(√3-√2,)=3(2√3)^2-11(3-2)^2=36-11=25...

千问 · 2012-12-23 19:56:37

3x2-5xy+3y2=3(x-y)2+xy=3(2√2)2+3-2=23...

已知x=√3+√2,y=√3-√2,求代数式3x²-5xy+3y²的值 要过程