Question

Докажите тождество ( х+y)(x+b)=x^2+(y+b)x+yb

Answer 1

( x + y )( x + b ) = x^2 + xb + xy + yb 
x^2 + ( y + b )x + yb = x^2 + xy + xb + yb 
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x^2 + xb + xy + yb = x^2 + xb + xy + yb