line eqns: why is ans. in standard form either pos. or neg.?

[psharris98]

when using point slope form for example : Slope 7 through (4,6), why is the answer in standard form either a negative or a positive. how will I know the difference. thanks...

psharris :?:

 

[skeeter]

why is the answer in standard form either a negative or a positive. how will I know the difference.

I really do not know what you are asking for w/regard to positive and negative. However, this is what I would do ...

slope = 7

point is x₁ = 4, y₁ = 6

point slope form is y - y₁ = m(x - x₁)

y - 6 = 7 (x - 6)

change to standard form (Ax + By = C), where A is normally written > 0 ...

y - 6 = 7x - 42

-7x + y = -36

7x - y = 36

 

[psharris98]

y - 6 = 7x - 42

-7x + y = -36

7x - y = 36

in the answer y-6=7x-42, I understand how you got this answer, why did 7x become negative 7x? and why did y become minus y
thanks...

it has been a long long time since I have taken algebra

 

[tkhunny]

It is implied subtraction. The terms didn't just "become" something else.

If
a = 7

Subtract 7 from each side

a - 7 = 7 - 7

a - 7 = 0

The seven did not become -7, it was just subtraction.

 

[skeeter]

y - 6 = 7x - 42

subtract 7x and add 6 to both sides of the equation ...

y - 6 - 7x + 6 = 7x - 42 - 7x + 6

combine like terms ...

-7x + y = - 36

multiply both sides of the equation by (-1) to "change" signs ...

(-1)(-7x + y) = (-1)(-36)

7x - y = 36