Posted by Kelly on Saturday, January 21, 2012 at 2:52am.
Adam has a hockey rink in his backyard. The current dimensions are 10m by 20m. Adam wants to have a hockey tournament and needs to double the area of his hockey rink. How much must Adam increase each dimension if he wants to increase them the same amount?
- Math, Quadratics - Mac, Saturday, January 21, 2012 at 4:00am
Current area = 200m2 [10m x 20m]
New area = 400m2 [10y x 20y]
So, 400 = 200y2
So, y2= 2
So, y = 1.41
So, each side must be increased by a factor 0f 1.41 times.
I this correct or do they mean add the same length to each side?
- Math, Quadratics - Damon, Saturday, January 21, 2012 at 5:36am
same to each
(10+x)(20+x) = 400
200 + 30 x + x^2 = 400
x^2 + 30 x - 200 = 0
x = [ -30 +/- sqrt(900 + 800) ]/2
x = [ -30 +/- 10 sqrt 17 ] /2
x = -15 +/- 5 sqrt 17
x = 5.62
15.62 * 25.62 = 400 ok
- Math, Quadratics - Kelly, Saturday, January 21, 2012 at 8:09am
Hi Damon, I got the same answer as you up to the equation x^2 + 30x - 200=0, but after that I don't understand what happened after that.. where does the 900 and 800 come form? and why you do divide by 2? thanks
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