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Find the range of values of $x$ for which $|x - 4| \geq 2$, where $x \in \mathbb{R}$ - Leaving Cert Mathematics - Question 2 - 2016

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Find the range of values of $x$ for which $|x - 4| \geq 2$, where $x \in \mathbb{R}$. Solve the simultaneous equations: $$x^2 + xy + 2y^2 = 4$$ $$2x + 3y = -1.$$

Worked Solution & Example Answer:Find the range of values of $x$ for which $|x - 4| \geq 2$, where $x \in \mathbb{R}$ - Leaving Cert Mathematics - Question 2 - 2016

Step 1

Find the range of values of $x$ for which $|x - 4| \geq 2$

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Answer

To solve the inequality x42|x - 4| \geq 2, we can break it into two cases:

  1. Case 1: x42x - 4 \geq 2

    Solving this gives:
    x6x \geq 6

  2. Case 2: x42x - 4 \leq -2

    Solving this gives:
    x2x \leq 2

Combining these two cases, we find the range of values for xx:
x(,2][6,+)x \in (-\infty, 2] \cup [6, +\infty).

Step 2

Solve the simultaneous equations: $x^2 + xy + 2y^2 = 4$ and $2x + 3y = -1$

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Answer

We can solve these equations by substitution or elimination. We'll use substitution:

  1. From the second equation, express xx:
    x=3y+12x = -\frac{3y + 1}{2}

  2. Substitute this into the first equation:
    (3y+12)2+(3y+12)y+2y2=4\left(-\frac{3y + 1}{2}\right)^2 + \left(-\frac{3y + 1}{2}\right)y + 2y^2 = 4

    Expanding this gives:

    (3y+1)24(3y+1)y2+2y2=4\frac{(3y + 1)^2}{4} - \frac{(3y + 1)y}{2} + 2y^2 = 4

    In clearing the fractions by multiplying through by 4, we get:
    (3y+1)242(3y+1)y+8y2=16\frac{(3y + 1)^2}{4} - 2(3y + 1)y + 8y^2 = 16

    Continuing simplifies this down to a quadratic equation in yy, which can be solved to find the values of yy. From this, we can find corresponding xx values.

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