An algebra problem by Paul Ryan Longhas

Algebra Level 5

Find all possible value of 3 x + 2 3\sqrt{x} + 2 satisfying the equation ( 3 x + 2 ) ( x + 5 ) = 0 (3\sqrt{x} +2)(x+5) = 0 .

2 i 2^i 0 3 5 + 2 3\sqrt{-5} + 2 3 5 + 2 , 0 3\sqrt{-5} + 2, 0

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1 solution

Tom Engelsman
Nov 8, 2016

For the equation ( 3 x + 2 ) ( x + 5 ) = 0 (3\sqrt{x} + 2)(x + 5) = 0 to hold true, we require either one of two conditions to occur:

x + 5 = 0 x + 5 = 0 (i),

3 x + 2 = 0 3\sqrt{x} + 2 = 0 (ii)

Solving for x in (i) produces x = 5 x = -5 , which in turn yields the complex number 2 + 3 5 = 2 + 3 5 i 2 + 3\sqrt{-5} = 2 + 3\sqrt{5}i for (ii). However, solving for x in (ii) produces x = 2 3 \sqrt{x} = -\frac{2}{3} , which is never valid for non-negative x. Also, the original equation is rendered invalid for all x ( 0 , 5 ) ( 5 , ) x \in (0, -5) \cup (-5, \infty) and also when (ii) equals 2 i 2^{i} since a nonzero complex number will result under either of these conditions.

Hence, choice D is the best answer.

Why is this lvl. 5?????????????????

A Former Brilliant Member - 3 years, 1 month ago

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