pre calculus
posted by kim .
find an equation of the line that passes through the points
(0,0),(1,5)
and
(2,1),(0,3)

The first one is
slope = y1y2/x1x2
slope = m = (05/0+1 = 5
y = mx + b
Then put in one of the points to calculate b.
5 = 5(1) + b
5 = 5 + b
b = 0
So the line is
y= mx + b
y = 5x + 0 or y = 5x.
The other one is don the same way.
Check my work very carefully. 
is the other problem is
y=3x+0 
The first pair is very very easy.
Remember that a line that passes through the origin must be of the form:
y = mx
since the intercept is zero. You are told that this line passes through the origin and that the point (1, 5) satisfies the equation. You should be able to write the answerdown from there.
There are a couple of ways to do the second one. he twopoint formula is
(y  y1) / (x  x1) = (y2  y1) / (x2 x1)
(y  1) / (x  2) = (3  1) / (0  2)
(y  1) / (x  2) = 2
multiply across by x  2
y 1 = 2x  4
and you should be close enough to finish from there.