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# AQA Maths C1 Watch

1. I wanted to ask when would you inverse a gradient to make a line equation.
So if its perpendicular you do -1/m also when it it to the normal or tangent you do -1/m, but in parrallel you leave the gradient as is??????????
2. (Original post by MyNameIsJeff)
I wanted to ask when would you inverse a gradient to make a line equation.
So if its perpendicular you do -1/m also when it it to the normal or tangent you do -1/m, but in parrallel you leave the gradient as is??????????
Tangent to a curve and normal to a circle= same gradient.
Tangent to a circle and normal to a curve= reciprocal.
3. (Original post by Jakz007)
Tangent to a curve and normal to a curve= same gradient.
Tangent to a circle and normal to a curve= reciprocal.
is what i wrote in correct or is that wrong?????/
4. (Original post by MyNameIsJeff)
is what i wrote in correct or is that wrong?????/
Say we have a point on a curve of gradient m

The tangent to the curve at this point will also have gradient m

However, the gradient of the line perpendicular to this point will have gradient -1/m

In order to test whether or not to lines are perpendicular, when you multiply their gradients by each other you should get -1, if you do not then they are not perpendicular i.e.

m(1) = 2
m(2) = -1/2

2*(-1/2)= -1 therefore perpendicular

m(1) = 1/4
m(2)= 4

(1/4)*4 = 1 therefore not perpendicular.

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