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प्रश्न
The centre of a circle is (2a, a – 7). Find the values of a if the circle passes through the point (11, – 9) and has diameter `10sqrt(2)` units.
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उत्तर
By given condition,
Distance between the centre C(2a, a – 7) and the point P(11, – 9), which lie on the circle = Radius of circle
∴ Radius of circle = `sqrt((11 - 2a)^2 + (-9 - a + 7)^2` ...(i) `[∵ "Distance between two points" (x_1, y_1) "and" (x_2, y_2) = sqrt((x_2 - x_1)^2 + (y_2 - y_1)^2)]`
Given that, length of diameter = `10sqrt(2)`
∴ Length of radius = `"Length of diameter"/2`
= `(10sqrt(2))/2`
= `5sqrt(2)`
Put this value in equation (i), we get
`5sqrt(2) = sqrt((11 - 2a)^2 + (-2 - a)^2`
Squaring on both sides, we get
50 = (11 – 2a)2 + (2 + a)2
⇒ 50 = 121 + 4a2 – 44a + 4 + a2 + 4a
⇒ 5a2 – 40a + 75 = 0
⇒ a2 – 8a + 15 = 0
⇒ a2 – 5a – 3a + 15 = 0 ...[By fractorisation method]
⇒ a(a – 5) – 3(a – 5) = 0
⇒ (a – 5)(a – 3) = 0
∴ a = 3, 5
Hence, the required values of a are 5 and 3.
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Case Study -2
A hockey field is the playing surface for the game of hockey. Historically, the game was played on natural turf (grass) but nowadays it is predominantly played on an artificial turf.
It is rectangular in shape - 100 yards by 60 yards. Goals consist of two upright posts placed equidistant from the centre of the backline, joined at the top by a horizontal crossbar. The inner edges of the posts must be 3.66 metres (4 yards) apart, and the lower edge of the crossbar must be 2.14 metres (7 feet) above the ground.
Each team plays with 11 players on the field during the game including the goalie. Positions you might play include -
- Forward: As shown by players A, B, C and D.
- Midfielders: As shown by players E, F and G.
- Fullbacks: As shown by players H, I and J.
- Goalie: As shown by player K.
Using the picture of a hockey field below, answer the questions that follow:
What are the coordinates of the position of a player Q such that his distance from K is twice his distance from E and K, Q and E are collinear?
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If the point A(2, – 4) is equidistant from P(3, 8) and Q(–10, y), find the values of y. Also find distance PQ.
