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L is the circle with equation x2 + y2 = 4
P(3/2, root 7/2) is a point on L.

Find an equation of the tangent to L at the point P.
(3 marks)


Sagot :

The equation of the tangent to L at the point  p(3/2, [tex]\sqrt[/tex]7/2) will be equal to  y+[tex]\sqrt[/tex]7x/3=0

What is tangent?

A straight line or plane that touches a curve or curved surface at a point, but if extended does not cross it at that point.

It is given that the equation of a circle is given by:

[tex]x^2+y^2=4[/tex]

Slope formula: If a line passes through two points, then the slope of the line is

[tex]m=\dfrac{y_2-y_1}{x_2-x_1}[/tex]

The endpoints of the radius are O(0,0) and P( 3/2,[tex]\sqrt[/tex]7/2). So, the slope of the radius is

Now by putting the values in the formula:

[tex]m=\dfrac{\dfrac{3}{2}-0}{\dfrac{\sqrt{7}}{2}-0}[/tex]

[tex]m=\dfrac{3}{\sqrt{7}}[/tex]

Now the Product of slopes of two perpendicular lines is always -1.

Let the slope of tangent line l is m. Then, the product of slopes of line l and radius is -1.

[tex]m\times m_1=-1[/tex]

[tex]m_1\times \dfrac {3}{\sqrt{7}}=-1[/tex]

[tex]m_1=\dfrac{-\sqrt{7}}{3}}[/tex]

The slope of line l is -[tex]\sqrt[/tex]7/3 and it passes through point P(3/2,[tex]\sqrt[/tex]7/2). So, the equation of line l is

[tex]y-y_2=m(x-x_2)[/tex]

[tex]y-\dfrac{\sqrt{7}}{2}=\dfrac{-\sqrt{7}}{3}(x-\dfrac{3}{2})[/tex]

[tex]y-\dfrac{\sqrt{7}}{2}=\dfrac{-\sqrt{7}}{3}x-\dfrac{-\sqrt{7}}{3} \times \dfrac{3}{2})[/tex]

[tex]y=\dfrac{-\sqrt{7}}{3}x[/tex]

Hence the tangent to L at the point P will have a slope of  [tex]y=\dfrac{-\sqrt{7}}{3}x[/tex]

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