Posted by **Jacob** on Monday, September 22, 2008 at 10:27am.

Find the equation of the straight line joining

a)(4, 4) and ( 2, 0)

b)(3, -1), (5, 4)

i also need to know how you went about solving this problem so i can understand.. many thanks

- Math -
**bobpursley**, Monday, September 22, 2008 at 10:31am
take the generic straight line:

y=mx + b.

Put in the first point: (4,4)

4=4m+b let this be the equation 1)

put in the second point in the generic

0=2m+b

Now you have two equations, and two unknowns (m,b). Solve them. In this case subtract the second equation from the first, which yields

4=2m or m=2

This makes b=-4 check that.

- Math -
**Reiny**, Monday, September 22, 2008 at 11:47am
A slight variation of bobpursey's method for #2

slope = (4+1)/(5-3) = 5/2

let the equation be y = (5/2)x + b

sub in the point (5,4)

4 = 5/2(5) + b

8 = 25 + 2b

b = -17/2

so y = (5/2)x - 17/2

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