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In the diagram below, F (−1; 5) and G (x; y) are points on the circle with the centre at the origin - NSC Technical Mathematics - Question 2 - 2022 - Paper 2

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In the diagram below, F (−1; 5) and G (x; y) are points on the circle with the centre at the origin. FG is parallel to the y-axis. 2.1.1 Write down the coordinates ... show full transcript

Worked Solution & Example Answer:In the diagram below, F (−1; 5) and G (x; y) are points on the circle with the centre at the origin - NSC Technical Mathematics - Question 2 - 2022 - Paper 2

Step 1

Write down the coordinates of G.

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Answer

Given that G (x; y) lies on the circle centered at the origin, we can determine its coordinates based on F being at (-1, 5). Since FG is parallel to the y-axis, G will have the same y-coordinate as F, thus:

  • The coordinates of G are G (−1; y).
  • To find y, we can use the equation of the circle, derived from its radius:

x2+y2=r2x^2 + y^2 = r^2

Substituting F's coordinates gives us radius squared:

r2=(1)2+(5)2=1+25=26.r^2 = (-1)^2 + (5)^2 = 1 + 25 = 26.

Now substituting x = -1 in the circle's equation:

(1)2+y2=26(-1)^2 + y^2 = 26

ightarrow y^2 = 25 ightarrow y = 5 ext{ or } y = -5.$$ Thus, the coordinates of G are G (−1; 5) or G (−1; -5).

Step 2

Determine: The gradient of OF

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Answer

To find the gradient (m) of line segment OF (where O is the origin (0,0) and F is (-1, 5)), we use the formula:

m=y2y1x2x1m = \frac{y_2 - y_1}{x_2 - x_1}

Substituting O (0, 0) as (x_1, y_1) and F (−1, 5) as (x_2, y_2), we get:

m=5010=51=5.m = \frac{5 - 0}{-1 - 0} = \frac{5}{-1} = -5.

Thus, the gradient of OF is -5.

Step 3

Determine: The equation of the tangent to the circle at F in the form y = ...

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Answer

Using the point-slope form of a line equation, which is:

yy1=m(xx1)y - y_1 = m(x - x_1)

Where (x_1, y_1) are the coordinates of point F and m is the gradient. Using the coordinates F (−1, 5) and the gradient as -\frac{1}{5}, we substitute:

y5=15(x+1).y - 5 = -\frac{1}{5}(x + 1).

Simplifying:

ightarrow y = -\frac{1}{5}x + 5 - \frac{1}{5} ightarrow y = -\frac{1}{5}x + \frac{24}{5}.$$ Thus, the equation of the tangent at F is: $$y = -\frac{1}{5}x + \frac{24}{5}.$$

Step 4

Draw, on the grid, the graph defined by: \( \frac{x^2}{7} + \frac{y^2}{64} = 1 \)

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  1. Identify the major and minor axes:

    • The equation indicates the ellipse has a semi-major axis of 8 (since ( \sqrt{64} = 8 )) and a semi-minor axis of approximately 2.645 (since ( \sqrt{7} \approx 2.645 )).
  2. Plot the intercepts:

    • For the x-intercepts, set y = 0:

    x27=1    x2=7    x=±7.\frac{x^2}{7} = 1 \implies x^2 = 7 \implies x = \pm\sqrt{7}.

    • For the y-intercepts, set x = 0:

    y264=1    y2=64    y=±8.\frac{y^2}{64} = 1 \implies y^2 = 64 \implies y = \pm8.

  3. Draw the ellipse, ensuring symmetry about both axes and including all intercepts marked clearly on the graph.

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