Evaluate 203 + (-9)3 + (-11)3
- AOption (a)
5930
- BOption (b)
5950
- COption (c)
5940
- DOption (d)
5992
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Correct answer
5940
Why this answer is correct
Shortcut Trick
Use the algebraic identity: If a + b + c = 0, then a3 + b3 + c3 = 3abc.
Here, a = 20, b = −9, and c = −11.
Sum = 20 + (−9) + (−11) = 20 − 20 = 0.
∴ 203 + (−9)3 + (−11)3 = 3 × 20 × (−9) × (−11) = 60 × 99 = 5940.
∴ The correct answer is 5940.
Alternate Method
Given: 203 + (−9)3 + (−11)3
Formula Used: Direct calculation of cubes.
⇒ 203 = 20 × 20 × 20 = 8000
⇒ (−9)3 = (−9) × (−9) × (−9) = −729
⇒ (−11)3 = (−11) × (−11) × (−11) = −1331
⇒ 8000 + (−729) + (−1331)
⇒ 8000 − (729 + 1331)
⇒ 8000 − 2060
⇒ 5940
∴ The correct answer is 5940.
Additional Information
Special Algebraic Identity
The conditional identity states that if a + b + c = 0, then the sum of their cubes is exactly 3abc.
General Cube Formula
a3 + b3 + c3 − 3abc = (a + b + c)(a2 + b2 + c2 − ab − bc − ca). This formula explains why the sum equals 3abc when the first factor is zero.
Negative Base Property
The cube of a negative number is always negative: (−x)3 = −(x3).