Multiply:
(i) x2+y2+z2-xy+xz+yzbyx+y-z
(ii) x2+4y2+z2+2xy+xz-2yzbyx-2y-z
(iii) x2+4y2+2xy+-3x+6y+9byx-2y+3
(iv) 9x2+25y2+15xy+12x-20y+16by3x-5y+4
(i) Given,
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Multiply the above expression by ( x+ y – z)
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=
= 
= 
(ii) Given,
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Multiply above expression by (x-2y-z)
Then ,
=
= 
By formula…
= 
iii) we have
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(iii) Given,
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Multiply above equation by ( x- 2y +3 )
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= 
= 
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(iv) Given,
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Multiply above equation by (3x – 5y +4)
We got,
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= 
= 
= 
16