Circle O has center (2, 6) and passes through the point P (4, 3). Write the equation of the line that is tangent to circle O at point P
A:y=3/2,x-3
B:y=2/3,x+1/3
C:y=-3/2,x+9
D:y=-2/3x+17/3

Respuesta :

First, fine the slope of the lines.

m=3-6/4-2
m=-3/2

To find the perpendicular slope of this, find the opposite reciprocal, or 2/3

Use formula y=mx+b to find the equation of this line.

3=(2/3)(4)+b
3=b+8/3
3-8/3=b+8/3-8/3
1/3=b

Now, plug in the values

y=2/3x+1/3, or B

The option (B) [tex]y=(\frac{2}{3} )x+(\frac{1}{3} )[/tex]  is the correct answer.

We have ,

Center of the circle, [tex]O(x1,y1)[/tex] ⇒ [tex]O(2,6)[/tex]

The point is [tex]P(x2,y2)[/tex] ⇒ [tex]P(4,3)[/tex]

The equation of line that is tangent to circle and point can be find by using the slope formula and equation of line.

Formula for slope, [tex]m=\frac{y2-y1}{x2-x1}[/tex]

On substituting the points,

[tex]m=\frac{3-6}{4-2}[/tex]

⇒[tex]m=\frac{-3}{2}[/tex]

The slope of the tangent is perpendicular to the slope of the line that passes through centre and on point of the circle.

So, the slope of tangent = [tex]-\frac{1}{m}[/tex]

⇒[tex]\frac{2}{3}[/tex]

Formula for equation of line, [tex]y=mx+b[/tex]

Now we need to find [tex]b[/tex] at [tex]P(4,3)[/tex]

⇒ [tex]3= (\frac{2}{3})4+b[/tex]

⇒[tex]3=(\frac{8}{3})+b[/tex]

⇒[tex]3-(\frac{8}{3} )=b[/tex]

⇒[tex]\frac{1}{3} =b[/tex]

Thus the equation of line, [tex]y=mx+b[/tex]

⇒ [tex]y=(\frac{2}{3} )x+(\frac{1}{3} )[/tex]

Hence, the option (B) is the correct answer.

Learn more about Equation of line and circles here:

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