7. Kamal gives the following proof that y−1=8/9(x+10) is the equation of a line that is tangent to a circle given by
(x+1)^2+(y−9)2=145.
The circle has center (−1,9) and radius 12.04. The point (−10,1) is on the circle because (−10+1)^2+(1−9)^2=(−9)^2+(−8)^2=145.
The slope of the radius is 9 − 1/−1 + 10=89; therefore, the equation of the tangent line is y−1=8/9(x+10).
a. Kerry said that Kamal has made an error. What was Kamal’s error? Explain what he did wrong.
b. What should the equation for the tangent line be?

Respuesta :

Answer with Step-by-step explanation:

We are given that equation of circle

[tex](x+1)^2+(y-9)^2=145=(\sqrt{145})^2[/tex]

Compare with equation of circle

[tex](x-h)^2+(y-k)^2=r^2[/tex]

Where (h,k)=Center of circle

r=Radius of circle

We get circle of center=(-1,9)

Radius=12.04

The point (-10,1) is on the circle because it satisfied the circle equation .

Slope of radius=[tex]\frac{1-9}{-10+1}=\frac{8}{9}[/tex]

By using slope formula

Slope:[tex]m=\frac{y_2-y_1}{x_2-x_1}[/tex]

We know that radius is perpendicular to the tangent.

When two lines are perpendicular then their slope is opposite reciprocal to each other.

Slope of tangent=[tex]-\frac{1}{\frac{8}{9}}=-\frac{9}{8}[/tex]

Now, the equation of tangent passing through the point(-10,1) with slope-9/8 is given by

[tex]y-1=-\frac{9}{8}(x+10)[/tex]

By using point-slope form

[tex]y-y_1=m(x-x_1)[/tex]

a.Kamal has made an error to find the slope of  tangent .

Slope of tangent=[tex]-\frac{9}{8}[/tex]

But he used slope of tangent 8/9

b.The equation  of tangent line

[tex]y-1=-\frac{9}{8}(x+10)[/tex]