In this activity, students interpret a quadratic equation in a situation. In the associated Algebra 1 lesson, students solve quadratic equations in situations. This activity supports students by helping them connect the equation to the situation. Making graphing technology available gives students an opportunity to choose appropriate tools strategically (MP5).

The purpose of the discussion is to connect the equation to the situation. Select students to share their solutions and statements. After each statement, ask another student if they agree that the statement is true and how they can know it is true based on the equation or graph. Here are some questions for discussion:

• “After a while, Diego’s plant shrinks to 0 centimeters tall. If this represents the time when the plant dies, what is an equation that could be solved to find the number of weeks after Diego begins nurturing the plant that the plant dies?” ( or )
• “What form is the equation given in? What information is easy to get from that form?” (The equation is given in vertex form. It is easy to get the vertex and not too difficult to find the -intercept in this form by substituting 0 for .)

The purpose of the discussion is to recall methods for solving systems of equations and the interpretation of the solution. Select students to share their solutions. After students share their solution for the coordinate of the intersection point, ask if any other students solved it using a different method. Here are some questions for discussion:

• “If Jada’s test grade was given by a quadratic function, like , would the intersection have the same meaning? Could the intersection be found using a method like graphing or substitution?” (Yes, the intersection has the same meaning, but there may be more than 1 intersection point or there may be no intersection points. Examining a graph or using a substitution method could be used to find any intersection points.)
• “What are some values of intersection points that do not make sense in this situation?” (If or if the function values are much greater than 100, the values do not make much sense. Negative values would represent negative study time, which is not reasonable. Similarly, intersections with function values greater than 100 would represent scores that are not reasonable unless the teacher is giving a lot of extra credit on both the quiz and the test.)