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Mathematics 14 Online
OpenStudy (aonz):

Help me please :( Find the points where the line x + 2y = 4 cuts the parabola y = (x − 1)^2, and show that the line is the normal to the curve at one of these points.

OpenStudy (anonymous):

Okie dokie, what is the definition of a line being normal to a curve? Write it out here so as to get everyone on the same page

OpenStudy (aonz):

when m1 m2 = -1?

OpenStudy (aonz):

where m1 and m2 are gradients?

OpenStudy (anonymous):

What's the gradient of each curve?

OpenStudy (aonz):

its 2x-2 and - 1/2

OpenStudy (anonymous):

2x-2 is the gradient of (x-1)^2 in general, but what is the gradient of the curve at the point of intersection?

OpenStudy (aonz):

gradient is 2

OpenStudy (anonymous):

Good, now we just need to verify that \[m _{1}m _{2} = -1\] Let us define \[m_{1} = 2\] and \[m _{2}=-\frac{ 1 }{ 2 }\] Take it from there

OpenStudy (whpalmer4):

The line intersects the parabola at (2,1) and at (-1/2,9/4). The former is the one where it is normal to the curve.

OpenStudy (aonz):

ok.. so the -1/2 is the one that is the normal?

OpenStudy (whpalmer4):

Former is the earlier one, latter is the later one

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