soumya1989 wrote:
If \(\sqrt{8x^2 +17} = 3x-2\), what is the value of 2x? _________________________
First square both sides of the equation to get: 8x² + 17 = (3x - 2)²
Expand and simplify right side: 8x² + 17 = 9x² - 12x + 4
Rearrange to get: 0 = x² - 12x - 13
Factor to get: 0 = (x - 13)(x + 1)
So,
x = 13 or
x = -1IMPORTANT: For square root equations we need to always CHECK for EXTRANEOUS roots by plugging them into the original equation.
x = 13√[8(13²) + 17] = 3(13) - 2
Simplify to get: √[some big POSITIVE number] = 37
The important thing here is that we are finding the square root of a POSITIVE value, AND the result is also POSITIVE. PERFECT!!
As such,
x = 13 is a valid solution
x = -1√[(8)((-1)²) + 17] = 3(-1) - 2
STOP
When we evaluate the RIGHT side, we get: √[(8)((-1)²) + 17] = -5
The square root of a value cannot equal -5
So, the solution
x = -1 is not valid
This means
x = 13 is the only valid solution.
Since the question asks for the value of 2x, the correct answer is
Cheers,
Brent