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Question
Math
Posted 3 months ago

The arrow diagram shows part of the function f:xax2+bx+cf: x \rightarrow a x^{2}+b x+c.
Find
(a) the values of a,ba, b and cc,
(b) the positive number xx whose image is 2 .
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Answer from Sia
Posted 3 months ago
Solution by Steps
step 1
We have the function f(x)=ax2+bx+cf(x) = ax^2 + bx + c and the mappings: f(2)=3f(-2) = -3, f(1)=6f(1) = 6, and f(3)=32f(3) = 32. We can set up the following equations:
1. $4a - 2b + c = -3$
2. $a + b + c = 6$
3. $9a + 3b + c = 32$
step 2
We can solve these equations simultaneously. First, we can eliminate cc by subtracting the second equation from the first and third equations:
From (1) - (2): $3a - 3b = -9 \implies a - b = -3$ (Equation 4)
From (3) - (2): $8a + 2b = 26 \implies 4a + b = 13$ (Equation 5)
step 3
Now we can solve Equations 4 and 5 together:
From Equation 4: $b = a + 3$
Substitute into Equation 5: $4a + (a + 3) = 13 \implies 5a + 3 = 13 \implies 5a = 10 \implies a = 2$
step 4
Substitute a=2a = 2 back into Equation 4 to find bb:
$b = 2 + 3 = 5$
step 5
Finally, substitute a=2a = 2 and b=5b = 5 into the second equation to find cc:
$2 + 5 + c = 6 \implies c = -1$
step 6
Now we have a=2a = 2, b=5b = 5, and c=1c = -1. To find the positive xx value whose image is 2, we set f(x)=2f(x) = 2:
$2x^2 + 5x - 1 = 2 \implies 2x^2 + 5x - 3 = 0$
step 7
We can use the quadratic formula to solve for xx:
$x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} = \frac{-5 \pm \sqrt{25 + 24}}{4} = \frac{-5 \pm 7}{4}$
This gives us $x = \frac{1}{2}$ (positive solution) and $x = -3$ (negative solution).
Answer
a = 2, b = 5, c = -1; positive x value is 12\frac{1}{2}
Key Concept
Finding coefficients of a quadratic function using given mappings and solving for specific function values.
Explanation
We determined the coefficients aa, bb, and cc by setting up equations based on the function's mappings and then solved for the positive xx value that results in an output of 2.

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