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# geometry

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Randy has a cube with an edge of 21 cm. From in the middle of one face of this cube Randy cuts out and removes a cube with an edge of 3 cm. Find the change in surface area of the original cube.

Oct 15, 2020

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Randy has a cube with an edge of a = 21 cm. From in the middle of one face of this cube Randy cuts out and removes a cube with an edge of b = 3 cm. Find the change in surface area of the original cube.

Hello Guest!

$$S_1=6a^2=6\cdot (21cm)^2$$

$$S_1=2646cm^2$$

$$\Delta S=-b^2+5b^2=4b^2=4\cdot (3cm)^2$$

$$\Delta S=36cm^2$$

$$The\ cube\ changes\ its\ Surface\ by\ 36\ cm ^ 2.$$

$$S_2=S_1+\Delta S=2646cm^2+36cm^2$$

$$S_2=2682cm^2$$

!

Oct 15, 2020