Archive
22nd of March 2017
Mathematics
Q:

Find the value of x3 + y3 - 12xy + 64 when x + y = 4

Nisha_vini29 - CBSE - Class IX

Wednesday, March 22, 2017 at 17:53:PM

A:

Hi Nisha,

Please check the signs. 

begin mathsize 16px style Given space straight x space plus space straight y space equals 4
Cubing space on space both space the space sides comma space we space get space
left parenthesis straight x space plus space straight y right parenthesis cubed space equals space 4 cubed space space
rightwards double arrow straight x cubed space plus space straight y cubed space plus space 3 xy left parenthesis straight x space plus space straight y right parenthesis space equals space 64 space
rightwards double arrow space straight x cubed space plus space straight y cubed space plus space 3 xy left parenthesis 4 right parenthesis space equals space 64 space space space
rightwards double arrow space space straight x cubed space plus space straight y cubed space plus 12 xy space minus space 64 space equals space 0 end style

Wednesday, March 22, 2017 at 18:09:PM