Angle Between Two Tangents

Rarely Tested

Angle Between Two Tangents

For the ellipse:

$$\frac{x^2}{a^2}+\frac{y^2}{b^2}=1$$

the angle between two tangents from an external point can be determined from the slopes $$m_1$$ and $$m_2$$ using:

$$\tan\theta=\left|\frac{m_1-m_2}{1+m_1m_2}\right|$$

Usage

- Used when the slopes of the two tangents are known or can be determined.

Question 1

Consider the ellipses given by $$x^2+4y^2=1$$ and $$4x^2+y^2=1$$.

Let $$P$$ be the point in the first quadrant where the given ellipses intersect. If $$\theta$$ is the acute angle between the tangents to the given ellipses at the point $$P$$, then the value of $$4\tan\theta$$ is ___.

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