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$$\begin{aligned}& y=x^{2}+3 x-7 \\& y-5 x+8=0\end{aligned}$$How many solutions are there to the system of equations above?

SAT · Math · previous-year question

  1. A.There are exactly 4 solutions.
  2. B.There are exactly 2 solutions.
  3. C.There is exactly 1 solution.correct
  4. D.There are no solutions.

Answer

C. There is exactly 1 solution.

Explanation

Choice $\mathbf{C}$ is correct. The second equation of the system can be rewritten as $y=5 x-8$. Substituting $5 x-8$ for $y$ in the first equation gives $5 x-8=x^{2}+3 x-7$. This equation can be solved as shown below:$$\begin{aligned}& x^{2}+3 x-7-5 x+8=0 \\& x^{2}-2 x+1=0 \\& (x-1)^{2}=0 \\& x=1\end{aligned}$$Substituting 1 for $x$ in the equation $y=5 x-8$ gives $y=-3$. Therefore, $(1,-3)$ is the only solution to the system of equations.Choice $A$ is incorrect. In the $x y$-plane, a parabola and a line can intersect at no more than two points. Since the graph of the first equation is a para

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