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huiyan's Question
Math
Posted 6 months ago
It is given that the graph of quadratic function f(x)=2x²+ kx+7 passes through the point (5,17).
(i) Calculate the value of k.
(ii) Find the equation of the axis of symmetry of the graph of quadratic
function.
(iii) Find the coordinates of the minimum point of the graph of the quadratic
function.
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Answer from Sia
Verified answer
Posted 6 months ago
Solution by Steps
step 1
To find the value of k k , we substitute the point (5,17) (5, 17) into the quadratic function f(x)=2x2+kx+7 f(x) = 2x^2 + kx + 7 : 2(5)2+k(5)+7=17 2(5)^2 + k(5) + 7 = 17
step 2
Simplifying the equation: 2(25)+5k+7=17 2(25) + 5k + 7 = 17 leads to 50+5k+7=17 50 + 5k + 7 = 17
step 3
Combining like terms gives 5k+57=17 5k + 57 = 17 . Subtracting 57 from both sides results in 5k=1757 5k = 17 - 57 , which simplifies to 5k=40 5k = -40
step 4
Dividing both sides by 5 yields k=8 k = -8
step 5
The equation of the axis of symmetry for a quadratic function ax2+bx+c ax^2 + bx + c is given by x=b2a x = -\frac{b}{2a} . Here, a=2 a = 2 and b=8 b = -8
step 6
Substituting the values gives x=82(2)=84=2 x = -\frac{-8}{2(2)} = \frac{8}{4} = 2
step 7
To find the coordinates of the minimum point, we substitute x=2 x = 2 back into the function f(x)=2x2+kx+7 f(x) = 2x^2 + kx + 7 : f(2)=2(2)2+(8)(2)+7 f(2) = 2(2)^2 + (-8)(2) + 7
step 8
Simplifying gives f(2)=2(4)16+7=816+7=1 f(2) = 2(4) - 16 + 7 = 8 - 16 + 7 = -1 . Thus, the minimum point is (2,1) (2, -1)
Answer
(i) k=8 k = -8 , (ii) Axis of symmetry: x=2 x = 2 , (iii) Minimum point: (2,1) (2, -1)
Key Concept
The axis of symmetry and minimum point of a quadratic function are derived from its coefficients.
Explanation
The value of k k was found by substituting the given point into the quadratic equation, and the axis of symmetry and minimum point were calculated using standard formulas for quadratic functions.

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