SOLUTION: What is the width of a uniform expansion needed all around to double the area of a 10cm by 15cm rectangle

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Question 459813: What is the width of a uniform expansion needed all around to double the area of a 10cm by 15cm rectangle
Answer by mananth(16946) About Me  (Show Source):
You can put this solution on YOUR website!
Let x be the expansion on all sides.
length & width will increase by 2x
(10+2x)(15+2x)=300
150+20x+30x+4x^2=300
4x^2+50x+150=300
4x^2+50x-150=0
2x^2+25x-75=0
Find the roots of the equation by quadratic formula

a= 2 ,b= 25 ,c= -75

b^2-4ac= 625 - 600
b^2-4ac= 1225
sqrt%28%091225%29=35
x=%28-b%2B-sqrt%28b%5E2-4ac%29%29%2F%282a%29
x1=%28-b%2Bsqrt%28b%5E2-4ac%29%29%2F%282a%29
x1=(-25+ 35)/4
x1=2.5
x2=(-25 -35)/4
x2= -15
Ignore negative value
x=2.5 the expansion