coordinate geometry ! (1 Viewer)

[darshil]

Hey everyone, i was just working on some straight line questions and came across these that I dont get. I must thank you beforehand for helping people like us out.

1) find the equation of the line given the x intercept=2 and y intercept=-5

2) (-1,2) is on ax-4y+11... Find a

Thanks everyone!

PS: what is a perpendicular bisector?

 

[annabackwards]

Hey everyone, i was just working on some straight line questions and came across these that I dont get. I must thank you beforehand for helping people like us out.

1) find the equation of the line given the x intercept=2 and y intercept=-5

2) (-1,2) is on ax-4y+11... Find a

Thanks everyone!

PS: what is a perpendicular bisector?

1/ y - y1 = m ( x - x1) where m = (y2 - y1)/(x2 - x1)
So since they're x and y intercepts, (x1, y1) = (2,0) and (x2,y2) = (0, -5).
Subbing that into the equation above we get:
y - 0 = (-5 - 0)( x - 2)/(0 - 2)
y = (5/2)(x-2)
y = 5x/2 -5 is the equation of the line.
(in general form it is 5x - 2y - 10 = 0 by rearranging)

2/ If a point lies on the line, just sub in the point and make a the subject.
a(-1) - 4(2) + 11 = 0
a = -8 + 11
a = 3

A perpendicular bisector is a line that bisect another line and is also perpendicular to it. In the instance below, the line through AB is a perpendicular bisector because it is perpendicular to AB and also bisects it (cuts it in half)

 

[jet]

You can see how CD divides AB in two, whilst they are perpendicular. CD is the perpendicular bisector of AB,

 

[darshil]

thanks for the replies, i appreciate it like nothing else.

 

[Drongoski]

I think Q1 was intended to be done via the intercept-form formula, viz:

 

[jet]

I think Q1 was intended to be done via the intercept-form formula, viz:

I thought about that, but then thought that I, and most other people would never use that formula anyway.

 

[Drongoski]

I thought about that, but then thought that I, and most other people would never use that formula anyway.

I understand. Of the std forms, 'y = mx + b" and "Ax + By + C = 0" are the most useful forms; intercept form of limited use.

 

[darshil]

the intercept formula wasnt even listed in fitzpatrick 2 unit workbook )=

 

[annabackwards]

the intercept formula wasnt even listed in fitzpatrick 2 unit workbook )=

Don't worry. I think i've seen that formula about twice in my life but i've never used it.

I understand. Of the std forms, 'y = mx + b" and "Ax + By + C = 0" are the most useful forms; intercept form of limited use.

I find the intercept form quite useful because it shows me to gradient and the y-intercept of the equation right away... but then again i've generally always used the intercept form.

 

[Drongoski]

annabackwards . . . I think u meant "gradient intercept form" rather than the "intercept form"

 

[annabackwards]

annabackwards . . . I think u meant "gradient intercept form" rather than the "intercept form"

Yeah, that's what i mean. "Intercept form" is just shorter and you can't really mix up gradient intercept form with general form anyway XD