SOLUTION: find the number such that its square is 21 more than four times the original number

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Question 696759:

find the number such that its square is 21 more than four times the original number
Answer by checkley79(3341) About Me  (Show Source):
You can put this solution on YOUR website!
X^2=21+4X
X^2-4X-21=0
(X-7)(X+3)=0
X-7=0
X=7 ANS.
X+3=0
X=-3 ANS.
PROOF:
7^2=21+4*7
49=21+28
49=49
AND.
-3^2=21+4*-3
9=21-12
9=9