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Mathematics 13 Online
OpenStudy (anonymous):

-3>1/3r

OpenStudy (campbell_st):

1st thing to identify is r cannot equal zero. multiply both sides by 3r -9r > 1 divide by -9 r < -1/9

OpenStudy (phi):

This is a bit tricky \[-3 > \frac{1}{3r} \] add 3 to both sides, so that we are comparing the expression to zero \[ 0 > 3+\frac{1}{3r} \] add the two terms \[ 0> \frac{9r+1}{3r} \] multiply both sides by 3r \[ 0 > 3r(9r+1) \] the 3 does not change the sign, so divide by 3 \[ r(9r+1)< 0\] this expression is negative (less than zero) if (a) both (r<0) and (9r+1)>0 (b) both (r>0) and (9r+1)<0 case (a) gives: \[ -\frac{1}{9}<r<0 \] case (b) requires that r>0 and simultaneously r < -1/9 i.e. no solution so the answer is \[ -\frac{1}{9}<r<0 \]

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