Question
Quantitative Aptitude Question on Basic Algebra
If a2+b2=89 and a2-b2=39, then find the value of a3 - b3-3ab, (a, b >0).
A
272
B
281
C
253
D
267
Answer
267
Explanation
Solution
The correct option is (D): 267.
a2 + b2 = 89........ (1)
a2 - b2= 39........ (2)
From (1) and (2):
a2 = 64 => a = 8
b2 = 25 => b = 5
Now,
a3 - b3 - 3ab
= 83 - 53 - 3 * 8 * 5
= 512 - 125 – 120
= 267.