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The square of the length of a space diagonal of a closed cube is 2175 cm2. What is the total surface area (in cm2) of the cube?
4305
4350
4530
4272
4350
Since the space diagonal squared d2=3a2 and total surface area S=6a2, notice that S=2×d2=2×2175=4350 cm2.
Square of the length of space diagonal of a closed cube = 2175 cm²
d2=3a2,Surface Area=6a2
Since the space diagonal squared d2=3a2 and total surface area S=6a2, notice that S=2×d2=2×2175=4350 cm2.
Students often find the square root to get d or a which can lead to rounding errors or unnecessary steps. Using the direct ratio S=2d2 saves time and prevents calculation errors.
Step 1: Understand the formula for cube space diagonal
The space diagonal d of a cube with edge length a is given by d=a3. Squaring both sides gives the square of the space diagonal: d2=3a2.
d2=3a2=2175
Step 2: Relate total surface area to a2
The total surface area S of a cube with 6 square faces of side a is S=6a2.
S=6a2
Step 3: Calculate the total surface area
Since 3a2=2175, we can find 6a2 by multiplying by 2: S=2×3a2=2×2175=4350 cm2.
S=2×2175=4350 cm2
B is correct because the total surface area of the cube is calculated as twice the square of its space diagonal (2×2175=4350 cm2).
Similar ratios exist for cuboids and regular tetrahedrons, where geometric proportions simplify calculations without needing to find individual edge dimensions.