Present

Gift box has rectangular shape with dimensions of 8×8×3 cm. Miloslav wants to cover with square paper with sides of 18 cm. How much paper left him?

Result

x =  100 cm²

Solution:

$d = 18 \ cm \ \\ S_{ 1 } = d \cdot \ d = 18 \cdot \ 18 = 324 \ cm^2 \ \\ \ \\ a = 8 \ cm \ \\ b = 8 \ cm \ \\ c = 3 \ cm \ \\ \ \\ S_{ 2 } = 2 \cdot \ (a \cdot \ b + a \cdot \ c + b \cdot \ c) = 2 \cdot \ (8 \cdot \ 8 + 8 \cdot \ 3 + 8 \cdot \ 3) = 224 \ cm^2 \ \\ \ \\ x = S_{ 1 } - S_{ 2 } = 324 - 224 = 100 = 100 \ cm^2$

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