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Re: If |y| ≤ -4x and |3x - 4|= 2x + 6. Which of the following could be the
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18 Nov 2019, 23:37
This is a very good question which tests your fundamental understanding of the concepts of Absolute Values.
The fact that the absolute value of a number cannot be negative is a very useful fact. If you do not leverage this fact, you can miss out on the most crucial piece of the puzzle.
|y| < -4x. We know that |y| can never be negative; or in other words, it is always greater than or equal to ZERO. But, in the inequality, we have a negative sign. This can only mean that x HAS to be non-positive so that -4x becomes non-negative.
Therefore, x CANNOT take any positive values. Basis this inference, we can eliminate answer options D and E straight away. We are left with options A, B and C.
Beyond this stage, the best and the most efficient method of solving this question would be to plug in each of the values from the options and check which value satisfies the equation. Also, from the expression inside the modulus, we can estimate that a fractional value of x is more probable in satisfying the equation. Therefore, I’d try the negative fractions first rather than trying the -3 in option A.
When we plug in the options, we see that option C satisfies the equation. The correct answer option is C.
The most important data in this question was the fact that |y| < -4x because it led us to the conclusion that x CANNOT be positive. Do not get confused as to what is the role of the variable ‘y’ in this question. It doesn’t serve any other purpose than telling us that |y| cannot be negative.
Hope that helps!