Answer:
The dimensions of the original cube are 16 in x 16 in x 16 in
Step-by-step explanation:
Let
x ----> the length side of the original cube
The surface area of the cube is equal to
[tex]SA=6b^2[/tex]
where
b is the length side of the cube
we know that
The dimensions of a cube are reduced by 4 inches on each side and the surface area of the new cube is 864 square inches
so
The length side of the new cube is
[tex]b=(x-4)\ in[/tex]
substitute in the formula of surface area
[tex]SA=6(x-4)^2[/tex]
[tex]SA=864\ in^2[/tex]
so
[tex]6(x-4)^2=864[/tex]
Simplify
[tex](x-4)^2=144[/tex]
take square root both sides
[tex](x-4)=(+/-)12[/tex]
[tex]x=4(+/-)12[/tex]
[tex]x=4(+)12=16\ in[/tex]
[tex]x=4(-)12=-8\ in[/tex] ----> the length side cannot be a negative number
therefore
The dimensions of the original cube are 16 in x 16 in x 16 in
