Bunuel
Is x < 0 ?
(1) x^5 < x^6
(2) 5^x > 6^x
We want to find if x lies to the left of 0 on a number line.
Statement 1\(x^5 - x^6 < 0\)
\(x^5(1-x) < 0\)
We see that the product of two numbers is negative, there can be two possible cases
Case 1: - \(x^5 < 0\)
- \((1 - x) > 0\)
As \(x^5 < 0; x < 0\)
1 - x > 0
- x > -1
x < 1
Combined, x < 0
Case 2: - \(x^5 > 0\)
- \((1 - x) < 0\)
As \(x^5 >0; x > 0\)
(1-x) < 0
-x < -1
x > 1
Combined x > 1
So this equation hold true in two regions, x < 0 and x > 1.
As we're getting two regions, we can rule out statement 1 and eliminate A and D.
Statement 2\(5^x > 6^x\)
\(6^x\) is positive, hence we can divide both sides on \(6^x\) without any change in the inequality sign
\((\frac{5}{6})^x\) > 1
Note that \(\frac{5}{6}\) will have value between 0 and 1, but when that decimal is raised to power x, the action makes the value greater than one. This can only happen when x is negative.
Hence x < 0.
Sufficient.
Option B