{"id":6761,"date":"2021-10-21T13:56:11","date_gmt":"2021-10-21T08:26:11","guid":{"rendered":"https:\/\/mathemerize.com\/?p=6761"},"modified":"2021-10-25T01:16:15","modified_gmt":"2021-10-24T19:46:15","slug":"what-is-the-equation-of-common-tangent-to-the-parabola-y2-4ax-and-x2-4ay","status":"publish","type":"post","link":"https:\/\/mathemerize.com\/what-is-the-equation-of-common-tangent-to-the-parabola-y2-4ax-and-x2-4ay\/","title":{"rendered":"What is the equation of common tangent to the parabola \\(y^2\\) = 4ax and \\(x^2\\) = 4ay ?"},"content":{"rendered":"
The equation of tangent in slope form to \\(y^2\\) = 4ax is<\/p>\n
y = mx + \\(a\\over m\\)<\/p>\n
Now, if it is common to both parabola, it also lies on second parabola<\/p>\n
then \\(x^2\\) = 4a(mx + \\(a\\over m\\))<\/p>\n
\\(mx^2 – 4am^2 – 4a^2\\) = 0 has equal roots.<\/p>\n
then its discriminant is zero. i.e. \\(b^2-4ac\\) = 0<\/p>\n
\\(16a^2m^2 + 16a^2m\\) = 0<\/p>\n
m = -1<\/p>\n
Putting m = -1 in equation y = mx + \\(a\\over m\\) we get<\/p>\n
y = -x – a<\/p>\n
x + y + a = 0<\/p>\n
Which is the required equation of common tangent to both parabola.<\/p>\n
The slope of the line touching both the parabolas \\(y^2\\) = 4x and \\(x^2\\) = -32 is<\/a><\/p>\n Find the locus of middle point of the chord of the parabola \\(y^2\\) = 4ax which pass through a given (p, q).<\/a><\/p>\n Find the equation of the tangents to the parabola \\(y^2\\) = 9x which go through the point (4,10).<\/a><\/p>\n Find the value of k for which the point (k-1, k) lies inside the parabola \\(y^2\\) = 4x.<\/a><\/p>\n