Circles Flashcards

1
Q

Diametric form

A

(x-x1)(x-x2) + (y-y1)(y-y2) = 0

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2
Q

r =

A

√g^2 + f^2 - C

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3
Q

Power of a pt

A

S1 = x1^2 + y1^2 + 2gx1 + 2fy1 + C

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4
Q

If S1 > 0

A

pt lies out

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5
Q

Length of tangent

A

√S1

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6
Q

Intercept cut off by circle from x axis

A

2√g^2-C^2

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7
Q

Eqn of line

A

lx + my + n = 0

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8
Q

If r1+r2 < C1C2

A

circles don’t touch

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9
Q

If r1+r2>C1C2

A

Circles touch externally

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10
Q

If r1 + r2 = C1C2

A

Circles intersect at 2 pts

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11
Q

If r1-r2 = C1C2

A

Circles touch internally

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12
Q

If r1-r2 < C1C2

A

One circle in other

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13
Q

Common chord eqn

A

S1 - S2 = 0

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14
Q

director circle

A

x^2+y^2 = 2r^2

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15
Q

angle b/n circles cos(180-θ) =

A

[r1^2 + r2^2 - (C1C2)^2]/2r1r2

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16
Q

If 2 circles cut orthogonally

A

r1^2 + r2^2 = (C1C2)^2

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17
Q

No of common tangents

A

4 if they don’t touch
3 if they touch
2 if they intersect at 2 pts
1 if one is in other & touches
0 if one in other

18
Q

Eqn of tangent to circle

A

xx1 + yy1 = r^2

19
Q

Condition for line to be tangent to x^2 + y^2 = r^2

A

C^2 = r^2(1+m^2)

20
Q

Parametric eqns

A

x = rcosθ
y = rsinθ

21
Q

If e = 0

22
Q

If e = 1

23
Q

if e < 1

24
Q

For y^2 = 4ax

A

focus(a,0)
directrix x = -a
LR = 4a
focal dist = |x+a|

25
Parametric form for y^2 = 4ax
x = at^2, y = 2at
26
For x^2 = 4ay
Focus(0,a) directrix y = -a LR = 4a Focal dist |y+a|
27
Parametric form for x^2=4ay
x = 2at, y = at^2
28
Shift of vertex
(x-h)^2 = 4a(y-k)
29
Point of contact for y^2=4ax
x = a/m^2 , y = 2a/m
30
Point of contact for x^2=4ay
x = 2am, y = am^2
31
Eqn of tangent at (x1,y1) to y^2=4ax
yy1 = 2a(x+x1)
32
Eqn of normal at (x1,y1) to y^2=4ax
y-y1 = -y1(x+x1)/2a
33
For ellipse
Foci(a,0) e = c/a x = +-a/e LR = 2b^2/a c = √a^2-b^2
34
For ellipse, eqn of tangent
y = mx +- √a^2m^2+b^2 or mx +- √b^2m^2+a^2
35
Pt of contact for ellipse
-a^2m/c , b^2/c
36
auxillary circle
x^2 + y^2 = a^2
37
director circle for ellipse
x^2 + y^2 = a^2 + b^2
38
For hyperbola, eqn of tangent
C^2 = a^2m^2 - b^2
39
For hyperbola, pt of contact
+-a^2m/c, b^2/c
40
Director circle for hyperbola
x^2+y^2 = a^2 - b^2
41
In rectangular hyperbola, e =
√2