MHB How to Find Lines Tangent to a Parabola Passing Through a Given Point?

  • Thread starter Thread starter Kenny52
  • Start date Start date
  • Tags Tags
    Quadratic Tangent
Kenny52
Messages
1
Reaction score
0
Find the equation of the straight line(s) which pass through the point (1, −2) and is (are) tangent to the parabola with equation y = x2

No calculus is to be used.I can substitute the point into the equation for the straight line giving -2=m+c

And into the parabola (-2)2 = m+c

Not sure if this is getting me anywhere
 
Mathematics news on Phys.org
The family of lines passing through $(1,-2)$ is (using the point-slope formula):

$$y=m(x-1)-2$$

Now, we may substitute for $y$ in $y=x^2$ to obtain:

$$m(x-1)-2=x^2$$

Write in standard quadratic form:

$$x^2-mx+(m+2)=0$$

Since the line is tangent to the parabola, we require the discriminant to be zero:

$$m^2-4(1)(m+2)=0$$

$$m^2-4m-8=0$$

Application of the quadratic formula yields:

$$m=2\left(1\pm\sqrt{3}\right)$$

And so the two lines are:

$$y=2\left(1\pm\sqrt{3}\right)(x-1)-2$$

Here's a graph:

[DESMOS=-10,10,-10,10]y=x^2;y=2\left(1+\sqrt{3}\right)\left(x-1\right)-2;y=2\left(1-\sqrt{3}\right)\left(x-1\right)-2[/DESMOS]
 
Insights auto threads is broken atm, so I'm manually creating these for new Insight articles. In Dirac’s Principles of Quantum Mechanics published in 1930 he introduced a “convenient notation” he referred to as a “delta function” which he treated as a continuum analog to the discrete Kronecker delta. The Kronecker delta is simply the indexed components of the identity operator in matrix algebra Source: https://www.physicsforums.com/insights/what-exactly-is-diracs-delta-function/ by...
Fermat's Last Theorem has long been one of the most famous mathematical problems, and is now one of the most famous theorems. It simply states that the equation $$ a^n+b^n=c^n $$ has no solutions with positive integers if ##n>2.## It was named after Pierre de Fermat (1607-1665). The problem itself stems from the book Arithmetica by Diophantus of Alexandria. It gained popularity because Fermat noted in his copy "Cubum autem in duos cubos, aut quadratoquadratum in duos quadratoquadratos, et...
I'm interested to know whether the equation $$1 = 2 - \frac{1}{2 - \frac{1}{2 - \cdots}}$$ is true or not. It can be shown easily that if the continued fraction converges, it cannot converge to anything else than 1. It seems that if the continued fraction converges, the convergence is very slow. The apparent slowness of the convergence makes it difficult to estimate the presence of true convergence numerically. At the moment I don't know whether this converges or not.
Back
Top