Moreno Li
05/25/2023 · Primary School
The points \( (-2,2) \) and \( (3,-23) \) lie on the curve given by the equation \( y=a x^{2}+b x+4 \). Use an algebraic method to find the values of \( a \) and \( b \).
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To find the values of \( a \) and \( b \) in the equation \( y = ax^2 + bx + 4 \) using the given points \((-2,2)\) and \((3,-23)\), we can substitute the coordinates of these points into the equation and then solve the resulting system of equations.
Substitute the coordinates of the first point \((-2,2)\) into the equation:
\[ 2 = a(-2)^2 + b(-2) + 4 \]
\[ 2 = 4a - 2b + 4 \]
\[ 4a - 2b = -2 \]
Substitute the coordinates of the second point \((3,-23)\) into the equation:
\[ -23 = a(3)^2 + b(3) + 4 \]
\[ -23 = 9a + 3b + 4 \]
\[ 9a + 3b = -27 \]
Now, we have a system of two equations:
\[ 4a - 2b = -2 \]
\[ 9a + 3b = -27 \]
We can solve this system of equations to find the values of \( a \) and \( b \).
Solve the system of equations by following steps:
- step0: Solve using the substitution method:
\(\left\{ \begin{array}{l}4a-2b=-2\\9a+3b=-27\end{array}\right.\)
- step1: Solve the equation:
\(\left\{ \begin{array}{l}a=\frac{-1+b}{2}\\9a+3b=-27\end{array}\right.\)
- step2: Substitute the value of \(a:\)
\(9\times \frac{-1+b}{2}+3b=-27\)
- step3: Simplify:
\(\frac{9\left(-1+b\right)}{2}+3b=-27\)
- step4: Multiply both sides of the equation by LCD:
\(\left(\frac{9\left(-1+b\right)}{2}+3b\right)\times 2=-27\times 2\)
- step5: Simplify the equation:
\(-9+15b=-54\)
- step6: Move the constant to the right side:
\(15b=-54+9\)
- step7: Add the numbers:
\(15b=-45\)
- step8: Divide both sides:
\(\frac{15b}{15}=\frac{-45}{15}\)
- step9: Divide the numbers:
\(b=-3\)
- step10: Substitute the value of \(b:\)
\(a=\frac{-1-3}{2}\)
- step11: Simplify:
\(a=-2\)
- step12: Calculate:
\(\left\{ \begin{array}{l}a=-2\\b=-3\end{array}\right.\)
- step13: Check the solution:
\(\left\{ \begin{array}{l}a=-2\\b=-3\end{array}\right.\)
- step14: Rewrite:
\(\left(a,b\right) = \left(-2,-3\right)\)
The solution to the system of equations is \( a = -2 \) and \( b = -3 \).
Therefore, the values of \( a \) and \( b \) in the equation \( y = ax^2 + bx + 4 \) are \( a = -2 \) and \( b = -3 \).
Quick Answer
The values of \( a \) and \( b \) are \( a = -2 \) and \( b = -3 \).
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