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Suppose f(x) = ax^2 + bx + c, where a, b, c ∈ R. Suppose
f(1) = f(3) = 0 and f(0) = −3. What is b?

Sagot :

Answer:

Step-by-step explanation:

Given:  f(1)= f(3) = 0
Putting f(1) = a(1)^2 + b(1) + c

                 = a + b + c

Putting f(3) = a(3)^2 + b(3) + c

                  = 9a + 3b + c

Putting f(0)=a(0)^2 + b(0) + c = -3

                 = c = -3


putting c = -3 In equation (1) and equation (2) we get,


a + b - 3 = 0                              9a + 3b - 3 = 0

a + b = 3                                    3(3a+b) = 3

a = 3 - b                                       3a + b = 1

                                                   3(3-b) + b =  1            [Putting a = 3 - b ]
                                                     9 - 3b +b = 1

                                                      -2b = -8

                                                         b = 4

Answer:

b = 4

Step-by-step explanation:

To find the value of b in the quadratic function f(x) = ax² + bx + c, begin by substituting f(0) = -3, and solve for c:

[tex]f(0) = -3\\\\a(0)^2+b(0)+c=-3\\\\0+0+c=-3\\\\c=-3[/tex]

Substitute c = -3 into the function:

[tex]f(x) = ax^2+bx-3[/tex]

Now, substitute f(1) = 0 and f(3) = 0 into the function to form a system of equations:

[tex]f(1)=0\\\\a(1)^2+b(1)-3=0\\\\a+b-3=0[/tex]

[tex]f(3)=0\\\\a(3)^2+b(3)-3=0\\\\9a+3b-3=0[/tex]

So, the system of equations is:

[tex]\begin{cases}a+b-3=0\\9a+3b-3=0\end{cases}[/tex]

Rearrange the first equation to isolate a:

[tex]a+b-3=0\\\\a=3-b[/tex]

Substitute a = 3 - b into the second equation and solve for b:

[tex]9(3-b)+3b-3=0\\\\27-9b+3b-3=0\\\\24-6b=0\\\\6b=24\\\\b=4[/tex]

Therefore, the value of b is:

[tex]\Large\boxed{\boxed{b=4}}[/tex]