You can put this solution on YOUR website! x must be zero so 2x(a+b) = 0
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If you need an equation you could say:
ax=bx
x(a-b)=0
Either x = 0 or a-b=0
If a-b=0, a=b.
But we are told a does not equal b.
Therefore x must be zero.
Then 2x(a+b) = 2*0*(a+b) = 0
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Cheers,
Stan H.