Bunuel
FRESH GMAT CLUB CHALLENGE PROBLEM
If x is a prime number, what is the value of x + c?
(1) \(|a + b + c - 2x| + \sqrt{(x^2 - a - b - c)^2} = - |c|\)
(2) \(\sqrt{(a + b + c - 1 + x)^2} + |\frac{1}{1-x}- a - b - c| + \sqrt{c^2}=0\)
M35-67
Official Solution:If \(x\) is a prime number, what is the value of \(x + c\)? (1) \(|a + b + c - 2x| + \sqrt{(x^2 - a - b - c)^2} = - |c|\)
Re-write as: \(|a + b + c - 2x| + \sqrt{(x^2 - a - b - c)^2} + |c|=0\). We have that the sum of three
non-negative values (the absolute value of some number, the square root of some number and the absolute value of some number) is 0. This to be true, each of the three must be 0.
So:
(i) \(a + b + c - 2x=0\), which gives \(a + b + c=2x\);
(ii) \(x^2 - a - b - c=0\), which gives \(a + b + c=x^2\);
(iii) \(|c|=0\), which gives \(c=0\).
Equate (i) and (ii): \(2x=x^2\). This gives that \(x=0\) or \(x=2\). It's given that \(x\) is a prime number, so \(x=2\)
\(x + c=2+0=2\). Sufficient.
(2) \( \sqrt{(a + b + c - 1 + x)^2} + |\frac{1}{1-x}- a - b - c| + \sqrt{c^2}=0\)
Here we also have that the sum of three
non-negative values is 0. This to be true, each of the three must be 0.
So:
(i) \(a + b + c - 1 + x=0\), which gives \(a + b + c = 1 - x\)
(ii) \(\frac{1}{1-x}- a - b - c=0\), which gives \(a + b + c =\frac{1}{1-x}\)
(iii) \(c^2=0\), which gives \(c=0\).
Equate (i) and (ii): \(1 - x=\frac{1}{1-x}\). This gives that \((1-x)^2=1\).
Takes the square root: \(|1-x|=1\);
\(x=0\) or \(x=2\). It's given that \(x\) is a prime number, so \(x=2\)
\(x + c=2+0=2\). Sufficient.
Answer: D