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Chelsea12345

The gradient of the line perpendicular to 2y=cx-3 is -2. Find C?

Reply 1

RDKGames

Study Forum Helper

Original post by Chelsea12345

The gradient of the line perpendicular to 2y=cx-3 is -2. Find C?

Yeah, so if the gradient perp to this line is -2, then the gradient of this line must be 1/2. Get this line in the form of y=mx+c then do m=1/2 and solve for c.

Reply 2

atsruser

Original post by Chelsea12345

The gradient of the line perpendicular to 2y=cx-3 is -2. Find C?

1. Rewrite in the form

y=mx+c

2. Use the fact that if two perp. lines have gradients

m_1,m_2

then

m_1 m_2=-1

Reply 3

username1753569

Rearrange equation into the form y=mx+c, input your gradient into the equation (it will not be -2, rather the reciprocal) and then you should get a value for c.

Reply 4

Chelsea12345

Original post by RDKGames

Yeah, so if the gradient perp to this line is -2, then the gradient of this line must be 1/2. Get this line in the form of y=mx+c then do m=1/2 and solve for c.

i got the first bit but how do i solve for C? do i put the gradient back into the equation or something?

Reply 5

RDKGames

Study Forum Helper

Original post by Chelsea12345

i got the first bit but how do i solve for C? do i put the gradient back into the equation or something?

You create a linear equation with C being the only unknown and you solve for it. No substitution needed.

Reply 6

Chelsea12345

Original post by RDKGames

You create a linear equation with C being the only unknown and you solve for it. No substitution needed.

Thankyou!

Reply 7

RDKGames

Study Forum Helper

Original post by natsciguy

A line perpendicular to a line always has a negative reciprocal gradient.

If the gradient of the line is -2, then the negative reciprocal is -1/-2 or 1/2.

To get the equation in standard form (y=mx+c) we must divide through by 2 to get y=c/2x-1.

As c/2 is the gradient (as it is the coefficient of x) then 1/2=c/2. Therefore c=1.