Help me with my quadratics?
A rectangular skating rink measures 40m by 20m. It is to be doubled in area by extending each side by the same amount. Determine how much each side should be extended to one decimal.
So I’ve been at it for a while now and I keep getting the wrong answer! Here’s my work so far:
Let x represent the number of ms each side was extended by.
lw=A
(40+x)(20+x)=2(20)(40)
800+40x+20x+x^2=1600
x^2+60x-800=0
x=-b+-! -b^2-4ac
2a
x=-(60)+-!(60)^2-4(1)(-800)
2(1)
x=-60+-!3600+3200
2
x=-60+-!6800
2
1. x= -60+82.5
2
x= 22.5
2
x=11.25
2. x= -60 - 82.5
2
x= -142.5
2
x= -71.25 (INAD)
So judging by that, it should be extended by 11.25 ms but the answer is 5.6ms and I can’t think of what I did wrong. Help?
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