1. **State the problem:**
We are given the simultaneous equations:
$$\frac{3x}{2y + 5} + 2y = 1$$
and
$$4y + x = -6$$
We need to:
a) Show that $$4y^2 - 4y - 23 = 0$$
b) Use this quadratic to solve the simultaneous equations.
2. **Show that $$4y^2 - 4y - 23 = 0$$:**
From the second equation, express $$x$$ in terms of $$y$$:
$$x = -6 - 4y$$
Substitute this into the first equation:
$$\frac{3(-6 - 4y)}{2y + 5} + 2y = 1$$
Simplify numerator:
$$\frac{-18 - 12y}{2y + 5} + 2y = 1$$
Multiply both sides by $$2y + 5$$ to clear the denominator:
$$-18 - 12y + 2y(2y + 5) = 1(2y + 5)$$
Expand terms:
$$-18 - 12y + 4y^2 + 10y = 2y + 5$$
Combine like terms on the left:
$$4y^2 - 2y - 18 = 2y + 5$$
Bring all terms to one side:
$$4y^2 - 2y - 18 - 2y - 5 = 0$$
Simplify:
$$4y^2 - 4y - 23 = 0$$
This matches the required quadratic.
3. **Solve the quadratic equation:**
Use the quadratic formula:
$$y = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}$$
where $$a=4$$, $$b=-4$$, $$c=-23$$.
Calculate discriminant:
$$\Delta = (-4)^2 - 4 \times 4 \times (-23) = 16 + 368 = 384$$
Calculate roots:
$$y = \frac{4 \pm \sqrt{384}}{8} = \frac{4 \pm 8\sqrt{6}}{8} = \frac{4}{8} \pm \frac{8\sqrt{6}}{8} = 0.5 \pm \sqrt{6}$$
Approximate values:
$$y_1 = 0.5 + 2.45 = 2.95$$
$$y_2 = 0.5 - 2.45 = -1.95$$
4. **Find corresponding $$x$$ values:**
Recall $$x = -6 - 4y$$.
For $$y_1 = 2.95$$:
$$x_1 = -6 - 4(2.95) = -6 - 11.8 = -17.8$$
For $$y_2 = -1.95$$:
$$x_2 = -6 - 4(-1.95) = -6 + 7.8 = 1.8$$
**Final solutions:**
$$(x, y) = (-17.8, 2.95) \text{ and } (1.8, -1.95)$$
These satisfy the simultaneous equations.
Simultaneous Equations F08351
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