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49=3.14r*r
We move all terms to the left:
49-(3.14r*r)=0
We add all the numbers together, and all the variables
-(+3.14r*r)+49=0
We get rid of parentheses
-3.14r*r+49=0
We move all terms containing r to the left, all other terms to the right
-3.14r*r=-49
r=-49/1
r=-49
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