1) Se foloseste formula:
[tex] x^{2} - y^{2} =(x - y)(x + y)[/tex], deci:
16=2(x+y), de unde
x+y=16:2=8
2) [tex] (x - y + z)^{2} = x^{2} + y^{2} + z^{2} - 2xy - 2yz + 2xz[/tex], adica:
[tex] (x - y + z)^{2} = x^{2} + y^{2} + z^{2} +2(xz - xy - yz)[/tex]
[tex] 6^{2} [/tex]=26+2(xz-xy-yz), de unde:
xz-xy-yz=5
3) [tex] (x+y)^{3} = x^{3} + y^{3} +3 x^{2} y+3x y^{2} [/tex]
[tex] (x+y)^{3} = x^{3} + y^{3} +3xy(x+y)[/tex]
125=[tex] x^{3} + y^{3} [/tex]+3*6*5
[tex] x^{3} + y^{3} [/tex]=125-90=35
