Parabola Questions 2Bc51D
1. **Problem 34:** Find $q$ for the parabola $y = x^2 + px + q$ given that it touches the $x$-axis at $x=5$.
2. Since the parabola touches the $x$-axis at $x=5$, it means $x=5$ is a root with multiplicity 2 (the parabola is tangent to the axis).
3. The parabola can be written as $y = (x - 5)^2 = x^2 - 10x + 25$.
4. Comparing with $y = x^2 + px + q$, we get $p = -10$ and $q = 25$.
5. Among the options, none is 25, so check if the problem means the parabola passes through $x=5$ on the $x$-axis (i.e., $y=0$ at $x=5$).
6. Substitute $x=5$ into $y = x^2 + px + q$ and set $y=0$: $$0 = 25 + 5p + q$$
7. We need to find $q$ such that the parabola touches the $x$-axis at $x=5$, so the discriminant must be zero:
$$D = p^2 - 4q = 0 \\ q = \frac{p^2}{4}$$
8. From step 6, $q = -25 - 5p$.
9. Equate the two expressions for $q$:
$$\frac{p^2}{4} = -25 - 5p$$
10. Multiply both sides by 4:
$$p^2 = -100 - 20p$$
11. Rearrange:
$$p^2 + 20p + 100 = 0$$
12. Solve quadratic for $p$:
$$p = \frac{-20 \pm \sqrt{400 - 400}}{2} = \frac{-20}{2} = -10$$
13. Substitute $p = -10$ into $q = -25 - 5p$:
$$q = -25 - 5(-10) = -25 + 50 = 25$$
14. Since $q=25$ is not in options, check if the problem expects $q$ value from options given. Possibly a typo or misinterpretation.
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**Problem 35:** Find values of $a$ such that the vertex of parabola $y = x^2 - 2(a+1)x + 1$ lies below $y=\frac{4}{3}$ and the vertex of $y = ax^2 - x + d$ lies above $y=\frac{4}{3}$.
1. Vertex of $y = x^2 - 2(a+1)x + 1$ is at:
$$x_v = \frac{2(a+1)}{2} = a+1$$
2. Vertex $y$-coordinate:
$$y_v = (a+1)^2 - 2(a+1)(a+1) + 1 = (a+1)^2 - 2(a+1)^2 + 1 = - (a+1)^2 + 1$$
3. Condition vertex below $\frac{4}{3}$:
$$- (a+1)^2 + 1 < \frac{4}{3} \\ - (a+1)^2 < \frac{4}{3} - 1 = \frac{1}{3} \\ (a+1)^2 > -\frac{1}{3}$$
4. Since square is always non-negative, this is always true.
5. For the second parabola $y = ax^2 - x + d$, vertex at:
$$x_v = \frac{1}{2a}$$
6. Vertex $y$-coordinate:
$$y_v = a \left(\frac{1}{2a}\right)^2 - \frac{1}{2a} + d = \frac{1}{4a} - \frac{1}{2a} + d = -\frac{1}{4a} + d$$
7. Condition vertex above $\frac{4}{3}$:
$$-\frac{1}{4a} + d > \frac{4}{3}$$
8. Without $d$ value, cannot solve further. Possibly missing data.
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**Problem 36:** Find real $a$ such that parabola $y_1 = x^2 - x + a$ lies above $y_2 = x^2 - x - a^2$.
1. Subtract:
$$y_1 - y_2 = a + a^2$$
2. For $y_1$ to be above $y_2$, require:
$$a + a^2 > 0 \\ a(a+1) > 0$$
3. This inequality holds when:
$$a < -1 \quad \text{or} \quad a > 0$$
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**Problem 37:** Find $a$ such that graphs of $y = 2ax + 1$ and $y = (a-6)x^2 - 2$ do not intersect.
1. Set equal:
$$(a-6)x^2 - 2 = 2ax + 1$$
2. Rearrange:
$$(a-6)x^2 - 2ax - 3 = 0$$
3. Treat as quadratic in $x$:
$$A = a-6, B = -2a, C = -3$$
4. Discriminant:
$$D = B^2 - 4AC = 4a^2 - 4(a-6)(-3) = 4a^2 + 12(a-6) = 4a^2 + 12a - 72$$
5. For no intersection, require $D < 0$:
$$4a^2 + 12a - 72 < 0 \\ a^2 + 3a - 18 < 0$$
6. Solve quadratic inequality:
$$a = \frac{-3 \pm \sqrt{9 + 72}}{2} = \frac{-3 \pm 9}{2}$$
7. Roots:
$$a_1 = 3, a_2 = -6$$
8. Inequality holds between roots:
$$-6 < a < 3$$
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**Problem 38:** Find $t$ such that $f(x) = 3x^2 + 2tx - (t-1)^2$ satisfies $f(-1) = -2$.
1. Substitute $x = -1$:
$$f(-1) = 3(1) + 2t(-1) - (t-1)^2 = 3 - 2t - (t^2 - 2t + 1) = 3 - 2t - t^2 + 2t - 1 = 2 - t^2$$
2. Set equal to $-2$:
$$2 - t^2 = -2 \\ -t^2 = -4 \\ t^2 = 4 \\ t = \pm 2$$
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**Problem 39:** Find sum of coordinates of intersection points of $y = 4x^2 + 4x + 1$ and $y = 2x + 1$.
1. Set equal:
$$4x^2 + 4x + 1 = 2x + 1 \\ 4x^2 + 4x - 2x = 0 \\ 4x^2 + 2x = 0 \\ 2x(2x + 1) = 0$$
2. Roots:
$$x = 0, x = -\frac{1}{2}$$
3. Find $y$ for each:
- For $x=0$, $y=2(0)+1=1$
- For $x=-\frac{1}{2}$, $y=2(-\frac{1}{2})+1=0$
4. Sum of coordinates:
$$(0 + 1) + \left(-\frac{1}{2} + 0\right) = 1 - \frac{1}{2} = \frac{1}{2}$$
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**Problem 40:** Find range of $y = \sqrt{x - x^2}$.
1. Inside square root must be non-negative:
$$x - x^2 \geq 0 \\ x(1 - x) \geq 0$$
2. This holds for $0 \leq x \leq 1$.
3. Maximum of $x - x^2$ is at $x=\frac{1}{2}$:
$$x - x^2 = \frac{1}{2} - \left(\frac{1}{2}\right)^2 = \frac{1}{2} - \frac{1}{4} = \frac{1}{4}$$
4. So range of $y$ is:
$$[0, \sqrt{\frac{1}{4}}] = [0, \frac{1}{2}]$$
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**Problem 41:** Find range of $y = \sqrt{9 - x^2}$.
1. Inside root:
$$9 - x^2 \geq 0 \\ -3 \leq x \leq 3$$
2. Minimum value of $y$ is 0 at $x=\pm 3$.
3. Maximum value is $\sqrt{9} = 3$ at $x=0$.
4. Range is:
$$[0, 3]$$