Question

3/Cho x+y= 6 va x.y=8

 Tinh: a/ x^3 + y^3

b/x^2+y^2

Bai 4 : Chung to : 

x^2+6x+11>0 voi moi x

 

 

Answer 1

dng cho xin k nha ban

Answer 2

bài 3

a) x³+y³

=(x+y)(x²+y²-xy)

=(x+y)[(x+y)²-3xy]

=6.(6²-3.8)=72

mk ko biết nó đúng hay sai

Answer 3

a ta co x^3+y^3=(x+y)(x^2-xy+y^2)=6(x^2+2xy+y^2)-3xy=6(x+y)^2-3.8=6.36-18=198

b ta co x^2+y^2=x^2+y^2+2xy-2xy=(x+y)^2-2xy=36-16=20

bai 4 

ta co x^2+6x+11=x^2+6x+9+2=(x+3)^2+2

(x+3)^2luon >=0

suy ra (x+3)^2+2>0 voi moi x thuoc R