Maths Help

[Jamesdavid3]

1).Find the co-ordinates of the point A on the line x= -3 such that the line joining A to B(5,3) is perpendicular to the line 2x+5y =12.

2). Using the vertices A(2a,2b), B(-2c, 0), C(2c,0).
(i) prove that the medians of a triangle are concurrent. (a median is a line joining a vertex to a midpoint of the opposite sides; the lines are concurrent if they have a common point of intersection);
(ii) show that the centroid is 2a/3, 2b/3. (a centroid is the point of intersection of the medians).


Opps sorry for Edit, i entered the wrong question! its for my uni. thx

 

[Jamesdavid3]

lies!
that's gcse maths, what crappy uni are you at?!

Its not that hard but i wasnt there for the lesson.

i goto Oxford

 

[Jamesdavid3]

Ok, im guessing no1 can tell me, ill go ask in lesson when im back.

 

[Jamesdavid3]

So far i have got to..

2x+5y=12 is in another way y= (-2/5)x +12/5 so the slope of this line is -2/5.
If this line is perpendicular to line (AB) then, the slope of (AB) is 5/2.

the equation of line (AB) is: Y - Yb = slope (X - Xb) because B is a point of the line
thus y - 3 = 5/2(x - 5)
and if A is a point of x= -3 then it's x-coordinate is -3
let's find its y-coordinate by replacing its x-coordinate in the equation of (AB)

y - 3 = 5/2(-3 -5) which gives you y= -17

and A(-3; -17)

But i was told theres algebra errors in the first part, but its close..

 

[Jamesdavid3]

i think the answer is 17 anyway, cheers