Expert: Sherman D. - 5/7/2007

Question
HIya...i really want to understand the steps in solving these bellow..i have been working them out but it seems the arithmatics i am using maybe inappropiate...please advice...WILL YOU BE ABLE TO CLEARLY SHOW EACH STAGE..THANKS..


Question

Find the equation of the straight line passing through the points.

(i) (-2,3)and (-1,5)
(ii) (2,-4)and(4,-2)
(iii) (1,-2) and (-2,3)

Y2-Y1
-----  =
X2-X1

please advice
X2-X1

Answer
1.)
(-2,3) and (-1,5)

m = (5 - 3)/(-1 - (-2))
m = 2/1
m = 2

3 = 2(-2) + b
3 = -4 + b
b = 7

ANS : y = 2x + 7

-------------------------------------------

2.)
2,-4) and (4,-2)
m = (-2 - (-4))/(4 - 2)
m = (2/2)
m = 1

-4 = 2(1) + b
-4 = 2 + b
b = -6

ANS : y = x - 6

------------------------------------

3.)
(1,-2) and (-2,3)
m = (3 - (-2))/(-2 - 1)
m = (3 + 2)/(-2 + (-1))
m = (5/(-3))
m = (-5/3)

-2 = (-5/3)(1) + b
-2 = (-5/3) + b
-6 = -5 + 3b
3b = -1
b = (-1/3)

ANS : y = (-5/3)x - (1/3)

------------------------------------------------------------

in (x1,y1) and (x2,y2)

the slope(m) = (y2 - y1)/(x2 - x1)

so now just plug that in for y1 or y2 = m(x1 or y1) + b, then solve for b like i have.