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The dimensions of a chocolate box are: height = x+2 inches, length = 2x+5 inches, and width = 4x-1 inches. if the volume of the box is 605 cubic inches, what is the value of x?


I'm a bit stuck on this, so any help is appreciated. The work I have is:

(2x+5)*(4x-1)*(x+2) = 605

(8x^2 + 20x – 2x – 5) * (x + 2)

(8x^3 + 20x^2 – 2x^2 – 5x) + (16x^2 + 40x – 4x – 10)

Regroup

8x^3 + (20x^2 – 2x^2 + 16x^2) + (40x – 5x – 4x) – 10

8x^3 + 34x^2 + 31x – 10 = 605

+10 +10

8x^3 + 34x^2 + 31x = 615

42x^5 + 31x = 615

73x^6 = 615


But I'm not exactly sure about it.

This is my second time asking this.

Respuesta :

Answer:

x= 3 inches

Step-by-step explanation:

-The volume of a box is given by the formula:

[tex]V=lwh\\\\l-length\\w-width\\h-height[/tex]

-We are given the dimensions h=x+2, l=2x+5 and w=4x-1.

We substitute this values in the formula and equate to the volume value.

[tex]V=lwh\\\\605=(x+2)(2x+5)(4x-1)\\\\605=8x^3+34x^2+31x-10[/tex]

#We take the values to the same side and equate to zero;

[tex]8x^3+34x^2+31x-615=0\\\\\\\#Factor\\\\\\(x-3)(8x^2+58x+205)=0[/tex]

#Applying the zero factor principal to obtain the different values of x:

[tex](x-3)=0\\\\\therefore x=3\ \ \ \ \ \ ...i\\\\(8x^2+58x+205)=0[/tex]

#We use the quadratic formula to solve the two other values of x:

[tex](8x^2+58x+205)=0\\x=\frac{-b\pm\sqrt{b^2-4ac}}{2a}\\\\=\frac{-58\pm\sqrt{58^2-4\times 8\times 205}}{2\times 8}\\\\x=-3.625+3.533i \ and \ x=-3.625-3.533i[/tex]

The two other values are negatives. Ignore them since length cannot be a negative.

The only reasonable value of x is x=3

#We substitute in the formula to validate:

[tex]V=lwh\\\\=(x+2)(2x+5)(4x-1)\\\\=(3+2)(2*3+5)(4*3-1)\\\\=605[/tex]

Hence, the value of x is 3 inches