Question

Write an equation for a line through (1,-1) and (2,3)

Answer 1

y = 4x - 5

Explanation:

Use the point slope form and add in the ordered pairs
`(3 + 1)/(2 - 1)` , and once you solve this it equals
`(4)/(1)`, or just 4. Now you have the first part of your equation, y = mx + b, but now you have y = 4x + b. To find b, substitute the x and y values of one of the given ordered pairs in for x and y in the equation, and I am using (2,3). The equation now looks like this: 3 = 4(2) + b. Now solve: 3 = 8 + b

Subtract 8 from both sides to get -5 = b. Now you have a full equation: y = 4x -5