Answer: 24 ft by 12 ft by 12 ft
This represents the exterior length, width and height in that order.
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Work Shown:
The steps you have written so far are 100% correct.
From there, you multiply the interior width, length and height to get the interior volume 972. Solve for x
So,
(length)*(width)*(height) = volume
(2x-6)(x-6)(x-3) = 972
(2x-6)(x^2-9x+18) = 972
2x(x^2-9x+18)-6(x^2-9x+18) = 972
2x^3-18x^2+36x-6x^2+54x-108 = 972
2x^3-24x^2+90x-108 = 972
2x^3-24x^2+90x-108-972 = 0
2x^3-24x^2+90x-1080 = 0
2(x^3-12x^2+45x-540) = 0
x^3-12x^2+45x-540 = 0
From here, we can use the factor by grouping method
x^3-12x^2+45x-540 = 0
(x^3-12x^2)+(45x-540) = 0
x^2(x-12)+45(x-12) = 0
(x^2+45)(x-12) = 0
Setting each factor equal to 0 leads to....
- x^2+45 = 0 doesn't have any real valued solutions for x, since sqrt(-45) is a complex number. We'll ignore this case and move on.
- x-12 = 0 solves to x = 12
So x = 12 is the only solution here.
If x = 12, then we have these exterior dimensions:
- length = 2x = 2*12 = 24 ft
- width = x = 12 ft
- height = x = 12 ft
The outer dimensions are 24 ft by 12 ft by 12 ft
From that, the inner dimensions would be:
L = 24-6 = 18 ft
W = 12-6 = 6 ft
H = 12-3 = 9 ft.
Then note how L*W*H = 18*6*9 = 972 ft^3 to help confirm the answer.
