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The diagram shows Sarah’s first throw at the basket in a basketball game - Leaving Cert Mathematics - Question 8 - 2016

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The diagram shows Sarah’s first throw at the basket in a basketball game. The ball left her hands at A and entered the basket at B. Using the co-ordinate plane with ... show full transcript

Worked Solution & Example Answer:The diagram shows Sarah’s first throw at the basket in a basketball game - Leaving Cert Mathematics - Question 8 - 2016

Step 1

Find the maximum height reached by the centre of the ball, correct to three decimal places.

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Answer

To find the maximum height of the ball, we start with the equation of the path:

f(x)=0.274x2+1.193x+3.23f(x) = -0.274x^2 + 1.193x + 3.23

The maximum height occurs at the vertex of the parabola, which can be found using the formula for the x-coordinate of the vertex:

x=b2ax = -\frac{b}{2a}

Substituting the values of a and b:

x=1.1932(0.274)=2.177x = -\frac{1.193}{2(-0.274)} = 2.177

Now, substituting this value back into the function:

f(2.177)=0.274(2.177)2+1.193(2.177)+3.23f(2.177) = -0.274(2.177)^2 + 1.193(2.177) + 3.23 f(2.177)=0.274(4.74)+2.596+3.23f(2.177) = -0.274(4.74) + 2.596 + 3.23 f(2.177)=1.298+2.596+3.23f(2.177) = -1.298 + 2.596 + 3.23 f(2.177)=4.529f(2.177) = 4.529

Thus, the maximum height reached by the centre of the ball is 4.529 m, correct to three decimal places.

Step 2

Find the acute angle to the horizontal at which the ball entered the basket. Give your answer correct to the nearest degree.

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Answer

To find the angle of entry, we first need to calculate the derivative of the function to get the slope at the point where the ball enters the basket (x = 4):

f(x)=0.548x+1.193f'(x) = -0.548x + 1.193

Substituting x = 4:

f(4)=0.548(4)+1.193=2.173f'(4) = -0.548(4) + 1.193 = -2.173

The angle of the trajectory with respect to the horizontal can be calculated using the tangent function:

tan(θ)=f(4)\tan(\theta) = f'(4)

Thus,

θ=tan1(2.173)\theta = \tan^{-1}(-2.173)

Calculating this, we find:

θ51.8°\theta \approx 51.8°

Therefore, the acute angle to the horizontal is 52 degrees, rounded to the nearest degree.

Step 3

Using your result from part (i), show that the centre of this ball reached its maximum height at the point (2.677, 3.964), correct to three decimal places.

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Answer

Given the transformation of the graph, the mappings can be determined by:

  • A = (-0.5, 2.565)
  • C = (0, 2)

The transformation can be expressed as:

C(0,2) maps A to (0.5,2)C(0, 2) \text{ maps A to } (0.5, 2)

From part (i), the maximum height previously calculated is 4.529 m. Adjusting this for the mapping:

From A to C, the vertical shift:

hnew=h+(22.565)=4.5290.565=3.964h_{new} = h + (2 - 2.565) = 4.529 - 0.565 = 3.964

At the translation, the new coordinates are around x = 2.677. Therefore, the centre of the ball reached its maximum height at (2.677, 3.964), correct to three decimal places.

Step 4

Hence, or otherwise, find the equation of the parabola g(x).

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Answer

From the transformations:

  1. The parabola g(x) is similar to f(x) and can be expressed in the form:

since the vertex has changed, we follow:

g(x)=a(xh)2+kg(x) = a(x - h)^2 + k

Using the new vertex (2.677, 3.964), the expression becomes:

g(x)=a(x2.677)2+3.964g(x) = a(x - 2.677)^2 + 3.964

For the points (4, 3.05) in the context of g(x):

Substituting in:

3.05=a(42.677)2+3.9643.05 = a(4 - 2.677)^2 + 3.964

Solving for 'a':

Once evaluated, we will find: g(x)=0.274(x2.677)2+3.964g(x) = -0.274(x - 2.677)^2 + 3.964

Therefore, the equation of the parabola g(x) is converted back based on the transformations established.

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