Westonci.ca is your trusted source for accurate answers to all your questions. Join our community and start learning today! Get expert answers to your questions quickly and accurately from our dedicated community of professionals. Our platform offers a seamless experience for finding reliable answers from a network of knowledgeable professionals.

Show that the curve x = 7 cos(t), y = 4 sin(t) cos(t) has two tangents at (0, 0) and find their equations

Sagot :

The equations with tangents at (0,0) are [tex]y = \frac{4}{7} x[/tex] and

[tex]y = -\frac{4}{7} x[/tex].

In this question,

The curves are x = 7 cos(t), y = 4 sin(t) cos(t)

Two tangents at (0, 0)

In this case, the parametric derivative of x and y are expressed in terms of t.

The first derivative dy/dx can be expressed as

[tex]\frac{dy}{dx}=\frac{\frac{dy}{dt} }{\frac{dx}{dt} }[/tex]

Now, dy/dt is obtained by differentiate y with respect to t,

[tex]\frac{dy}{dt}= 4[cos(t)(cos(t))+sin(t)(-sin(t))][/tex]

⇒ [tex]\frac{dy}{dt}= 4[cos^{2} (t)-sin^{2} (t)][/tex]

Now, dx/dt is obtained by differentiate x with respect to t,

[tex]\frac{dx}{dt} =7(-sin(t))[/tex]

⇒ [tex]\frac{dx}{dt} =-7sin(t)[/tex]

Thus, [tex]\frac{dy}{dx}=\frac{4[cos^{2}(t)-sin^{2}(t ) ]}{-7sin(t)}[/tex]

At (0,0) x = 0 and y = 0, Then

0 = 7 cos(t)

0 = 4 sin(t) cos(t)

and

cos(t) = 0

sin(t) cos(t) = 0

There are two values between -π and π which satisfy these equations simultaneously are

t = π/2

t = -π/2

The equation of a straight line given a point and its slope is

y-y₀ = m(x-x₀)

The two tangents lies at (0,0), so the equation becomes

y = mx

Then the two straight lines will be

y = m₁x  and

y = m₂x

For t = π/2,

[tex]m_1=\frac{dy}{dx}=\frac{4[cos^{2}(\frac{\pi }{2} )-sin^{2}(\frac{\pi }{2} ) ]}{-7sin(\frac{\pi }{2} )}[/tex]

⇒ [tex]m_1=-\frac{4[0-1]}{7(1)}[/tex]

⇒ [tex]m_1=\frac{4}{7}[/tex]

For t = -π/2,

[tex]m_2=\frac{dy}{dx}=\frac{4[cos^{2}(-\frac{\pi }{2} )-sin^{2}(-\frac{\pi }{2} ) ]}{-7sin(-\frac{\pi }{2} )}[/tex]

⇒ [tex]m_2=-\frac{4[0-1]}{-7(1)}[/tex]

⇒ [tex]m_2=-\frac{4}{7}[/tex]

Thus the equations with tangents at (0,0) are [tex]y = \frac{4}{7} x[/tex] and

[tex]y = -\frac{4}{7} x[/tex].

Learn more about equation of curve here

https://brainly.com/question/9959935

#SPJ4