Systems of Polynomial Equations
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PSAT Math › Systems of Polynomial Equations
A designer models a ramp by the line $y=\tfrac{1}{2}x+1$ and an arch above it by the parabola $y=-\tfrac{1}{2}x^2+2x+1$. The ramp meets the arch at the intersection points. What is the product of the $x$-coordinates of the intersection points?
$0$
$2$
$8$
$4$
Explanation
We need the product of x-coordinates where the line y = ½x + 1 meets the parabola y = -½x² + 2x + 1. This system combines a line and parabola, solved by substitution. Setting ½x + 1 = -½x² + 2x + 1, we get ½x + 1 + ½x² - 2x - 1 = 0, which simplifies to ½x² - (3/2)x = 0, or ½x(x - 3) = 0. This gives x = 0 or x = 3, so the product of x-coordinates is 0 × 3 = 0. A key insight: when one root is zero, the product of all roots must be zero. For any quadratic ax² + bx + c = 0, Vieta's formula gives the product of roots as c/a, and here c = 0 confirms our answer.
On the coordinate plane, the graphs of the line $y=x+1$ and the parabola $y=x^2-1$ are shown. How many solutions does the system have (how many intersection points are there)?
0
1
2
3
Explanation
The question asks for the number of solutions to the system, which corresponds to the intersection points of the line and parabola. This is a system of one linear and one nonlinear equation, solved by substitution, emphasizing that a parabola and line can intersect 0, 1, or 2 times. Set x + 1 = x² - 1, rearrange to x² - x - 2 = 0, and factor as (x - 2)(x + 1) = 0, giving x = 2 and x = -1. These yield two distinct real solutions. A key error might be miscounting roots if the discriminant is overlooked, but here it's positive with two roots. A strategy is to calculate the discriminant quickly to determine the number of intersections without full solving.
A designer models the edge of a ramp with $y=x^2-4x+3$ and a support beam with $y=x-1$. At what points do the graphs intersect? Solve the system algebraically.
$(0,-1)$ and $(3,2)$
$(1,0)$ and $(4,3)$
$(2,1)$ and $(3,2)$
$(1,0)$ only
Explanation
The question seeks the intersection points of the quadratic ramp model and linear support beam. This system combines a linear and a nonlinear quadratic equation, solved via substitution, with the reminder that such graphs can intersect at 0, 1, or 2 points. Set x² - 4x + 3 = x - 1, simplify to x² - 5x + 4 = 0, and factor as (x - 1)(x - 4) = 0, so x = 1 and x = 4. Corresponding y-values are y = 0 for x = 1 and y = 3 for x = 4, giving (1, 0) and (4, 3). Errors often occur in algebraic simplification, like incorrect subtraction. When time is limited, graph mentally or check discriminants to confirm two real roots.
On the coordinate plane, the line $y=x+2$ and the parabola $y=x^2$ are graphed. How many solutions does the system have (that is, how many intersection points are there)?
0
1
2
3
Explanation
The question asks for the number of solutions to the system of y = x + 2 and y = x², which represents the intersection points of a line and a parabola on the coordinate plane. This system includes one linear and one nonlinear equation, solved by substitution: set x² = x + 2, rearrange to x² - x - 2 = 0, and factor as (x - 2)(x + 1) = 0, giving x = 2 and x = -1. These yield two distinct real solutions, confirming two intersection points. A key error could be incorrectly factoring the quadratic or overlooking the discriminant (here, 1 + 8 = 9 > 0, indicating two real roots). Note that a parabola and a line can intersect 0, 1, or 2 times, and in this case, it's two; a useful strategy is to calculate the discriminant of the resulting quadratic to quickly determine the number of solutions without fully solving.
A student solves the system $y=x^2+2x$ and $y=4x$ to find when a quadratic growth model matches a linear estimate. What is the product $x_1x_2$ of the $x$-values of all solutions?
$0$
$8$
$-8$
$-4$
Explanation
The question seeks the product x₁x₂ of x-values where quadratic and linear models match. This is a linear-nonlinear system, solved by substitution, with up to 2 intersections possible for line and parabola. Set x² + 2x = 4x, simplify to x² - 2x = 0, factor as x(x - 2) = 0, so x = 0 and x = 2, product 0. For ax² + bx + c = 0, product is c/a, here 0/1 = 0. A common error is ignoring the x=0 solution. Use quadratic properties like product of roots to answer without listing roots.
Solve the system algebraically: $$y=x^2-4x+1$$ and $$y=-x+3.$$ How many real solutions does the system have?
0
1
2
3
Explanation
We're asked to count the number of real solutions when y = x² - 4x + 1 intersects y = -x + 3. This system combines a parabola with a line, solved by substitution. Setting x² - 4x + 1 = -x + 3, we get x² - 4x + 1 + x - 3 = 0, which simplifies to x² - 3x - 2 = 0. Using the quadratic formula or factoring, we find the discriminant is (-3)² - 4(1)(-2) = 9 + 8 = 17 > 0, indicating two distinct real solutions. The key insight is that a positive discriminant means the line crosses the parabola at two points. When solving systems graphically or algebraically, remember that the number of solutions equals the number of intersection points.
A drone’s height is modeled by $y=x^2-6x+8$, while a safety limit is $y=0$. The drone is at the safety limit when the graphs intersect. How many solutions does the system have?$$\begin{cases}y=x^2-6x+8\\y=0\end{cases}$$
0
1
2
4
Explanation
The question asks how many solutions the system has, meaning how many times the drone's height model intersects the safety limit y=0. This involves setting a quadratic equal to a constant (horizontal line), solvable by finding roots of the quadratic equation, with 0, 1, or 2 possible intersections. Set $x^2 - 6x + 8 = 0$. Factor as $(x - 2)(x - 4) = 0$, giving $x = 2$ and $x = 4$, so two solutions. A common error is misfactoring or ignoring the constant term. A test-taking strategy is to compute the discriminant $(36 - 32 = 4 > 0)$ to confirm two real roots quickly.
A ball’s height $y$ (in meters) after $x$ seconds is modeled by $y=-x^2+6x+1$. A timing sensor also records the height as $y=2x+1$ over the same interval. At what point(s) $(x,y)$ do these two models agree (i.e., where do the graphs intersect)? Solve the system algebraically.
$(1,3)$ and $(5,11)$
$(1,3)$ only
$(0,1)$ and $(4,9)$
$(0,1)$ only
Explanation
The question asks for the points where two models of a ball's height agree, meaning the intersection points of the quadratic equation y = -x² + 6x + 1 and the linear equation y = 2x + 1. This is a system consisting of one linear and one nonlinear (quadratic) equation, which can be solved algebraically by setting the equations equal to each other. Set -x² + 6x + 1 = 2x + 1, subtract 2x + 1 from both sides to get -x² + 4x = 0, then multiply by -1 to obtain x² - 4x = 0, and factor as x(x - 4) = 0, yielding x = 0 or x = 4. Substitute these x-values back into y = 2x + 1 to find y = 1 when x = 0 and y = 9 when x = 4, so the points are (0, 1) and (4, 9). A common error is mishandling the signs during subtraction, which might lead to an incorrect quadratic equation. Remember that a line and a parabola can intersect at 0, 1, or 2 points, and here they intersect at two; for test-taking, verify solutions by plugging back into both original equations.
A ball’s height (in meters) after $t$ seconds is modeled by $h=-t^2+6t+1$. A nearby sensor reports the height is also given by the line $h=2t+1$. The ball and the sensor agree at the times when the graphs intersect. What are all solutions $(t,h)$ to the system?
$(1,3)$ and $(3,7)$
$(1,3)$ only
$(0,1)$ and $(2,5)$
$(0,1)$ and $(4,9)$
Explanation
We need to find where the ball's height h = -t² + 6t + 1 equals the sensor's reading h = 2t + 1. This is a system with a parabola (quadratic) and a line, which we solve by substitution. Setting -t² + 6t + 1 = 2t + 1, we get -t² + 6t + 1 - 2t - 1 = 0, which simplifies to -t² + 4t = 0, or -t(t - 4) = 0. This gives t = 0 or t = 4. When t = 0, h = 2(0) + 1 = 1, and when t = 4, h = 2(4) + 1 = 9, so our solutions are (0,1) and (4,9). A common error is forgetting to find the h-values after solving for t. Since we found two distinct intersection points, this confirms that a parabola and line can intersect at 0, 1, or 2 points.
A coach tracks a runner’s distance $y$ with two models: a curved estimate $y=x^2-6x+8$ and a linear estimate $y=-2x+4$, where $x$ is time. If $(x_1,y_1)$ and $(x_2,y_2)$ are intersection points, what is $x_1x_2$?
$$\begin{cases} y=x^2-6x+8 \\ y=-2x+4 \end{cases}$$
$4$
$0$
$-4$
$8$
Explanation
We need to find the product of x-coordinates where $y = x^2 - 6x + 8$ and $y = -2x + 4$ intersect. This quadratic-linear system uses substitution. Setting equal: $x^2 - 6x + 8 = -2x + 4$, which becomes $x^2 - 4x + 4 = 0$. This factors as $(x - 2)^2 = 0$, giving $x = 2$ as a repeated root. With only one x-value (multiplicity 2), we have $x_1 = x_2 = 2$, so $x_1 x_2 = 2 imes 2 = 4$. A common error is thinking one solution means the product is undefined, but a repeated root counts twice. For any quadratic $ax^2 + bx + c = 0$, the product of roots equals $c/a$, which here is $4/1 = 4$.