Math Problem Statement

Find the quadratic function of a graph that goes through (0,15), (3,0), (5,0)

Solution

To find the quadratic function that goes through the points (0,15)(0, 15), (3,0)(3, 0), and (5,0)(5, 0), we will use the general form of a quadratic equation:

y=ax2+bx+cy = ax^2 + bx + c

We are given the three points, which will allow us to create a system of equations.

  1. For the point (0, 15): When x=0x = 0, y=15y = 15: 15=a(0)2+b(0)+cc=1515 = a(0)^2 + b(0) + c \quad \Rightarrow \quad c = 15

  2. For the point (3, 0): When x=3x = 3, y=0y = 0: 0=a(3)2+b(3)+150=9a+3b+150 = a(3)^2 + b(3) + 15 \quad \Rightarrow \quad 0 = 9a + 3b + 15 This simplifies to:

\quad \text{(Equation 1)}$$ 3. **For the point (5, 0)**: When $$x = 5$$, $$y = 0$$: $$0 = a(5)^2 + b(5) + 15 \quad \Rightarrow \quad 0 = 25a + 5b + 15$$ This simplifies to: $$25a + 5b = -15 \quad \text{(Equation 2)}$$ Now, we solve this system of equations: ### Step 1: Solve for $$b$$ in terms of $$a$$ From Equation 1: $$9a + 3b = -15 \quad \Rightarrow \quad 3b = -15 - 9a \quad \Rightarrow \quad b = -5 - 3a$$ ### Step 2: Substitute $$b = -5 - 3a$$ into Equation 2 $$25a + 5(-5 - 3a) = -15$$ Simplify: $$25a - 25 - 15a = -15 \quad \Rightarrow \quad 10a - 25 = -15$$ Solve for $$a$$: $$10a = 10 \quad \Rightarrow \quad a = 1$$ ### Step 3: Solve for $$b$$ Substitute $$a = 1$$ into $$b = -5 - 3a$$: $$b = -5 - 3(1) = -8$$ ### Step 4: Write the quadratic function Now that we have $$a = 1$$, $$b = -8$$, and $$c = 15$$, the quadratic function is: $$y = x^2 - 8x + 15$$ This is the quadratic function

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Math Problem Analysis

Mathematical Concepts

Algebra
Quadratic Functions
System of Equations

Formulas

General form of a quadratic function: y = ax^2 + bx + c
Substitution into system of equations
Solving linear equations for variables

Theorems

System of Equations

Suitable Grade Level

Grades 9-11