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Originally Posted by

**scouser** actually this question was supposed to be simple. i was asked this question in a revision introduction to proof and reasoning. i was supposed to determine which of those little sign thingies connects the two statements, you know arrow to the left, arrow to the right, arrows on both sides. do you understand what i mean?

Hi **scouser**.

The relation between the two statements is “if and only if” (assuming that $\displaystyle a,b\in\mathbb R$ – which I’m sure is in mentioned in your book though you didn’t mention it in your first post). Thus:

$\displaystyle \forall\,a,b\in\mathbb R,\ (a,b)$ is on $\displaystyle y=2x-1\ \color{red}\iff\color{black}\ b=2a-1$