Let : A ≡ ( x1, y1 ) ≡ ( 4, - 4), B ≡ ( x2, y2 ) ≡ ( 9, -1 ).
Then, slope of line AB is
m = ( y₂ - y₁ ) / ( x₂ - x₁ ) = (-1 + 4 ) / ( 9 - 4 ) = 3/5
Hence, equation of line AB in Point-Slope Form is
y - y₁ = m ( x - x₁ )
y + 4 = (3/5) ( x - 4 ) .................... (1)
5y + 20 = 3x - 12
5y = 3x - 32
y = (3/5)x + (-32/5) ....................... (2)
This is the Slope-Intercept Form
y = mx + b.
The form which is easier to get is
Slope-Point Form. But this is one's
personal choice.
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You need two points before you can calculate the slope.
Point-slope form is just another way to express a linear equation. It uses two (any two points that fall on the line) and the slope of the line (Therefore the name point-slope form).y2 - y1 = m(x2 - x1)...with m as the slope.
that is one point, you need at least two for a line.
You need either a point and the slope of the line or two points. Then you use the point slope form of the line or the slope intercept form to write the lines.A given point has an infinite number of lines going through it, that is why you need more information.
In the case that you are using Slope-Intercept Form, no, you only plot two points: the y-intercept and one other point. If you don't use Slope-Intercept Form, then you have to use three points.