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To find a circle's radius given it's area, we can look at the formula for the area of a circle.
$A=πr_{2} $
In the case of our exercise, the area, $A,$ is $90cm_{2}$. We can set up our quadratic and solve for the radius, $r.$
Since we are computing length, we can disregard the negative root and say that the circle's radius, to the nearest tenth, is $5.4cm.$

$A=πr_{2}$

Substitute$A=90$

$90=πr_{2}$

Solve for $r$

DivEqn$LHS/π=RHS/π$

$π75 =r_{2}$

SqrtEqn$LHS =RHS $

$±π75 =r$

CalcRootCalculate root

$±5.35237...=r$

RearrangeEqnRearrange equation

$r=±5.35237...$