write an equation in point-slope form for the line through the given point with the given slope.(-3, -5); m = -2/5

Question

mrnood · Answer

you know the 'point slope' form is 

y=mx+b

and you are told m

so the equation is

y= -2/5  x +b

but you also know that when x= -3 then y = -5

so 
-5 = -2/5 (-3) + b

so oyu can work out b

and there is your answer

er.mohd.amir · Answer

point slope form y-y1=m(x-x1)  where m is slope and (x1,y1) is point.

mathstudent55 · Answer

A line with slope m, that passes through and point $(x_1, y_1)$
has the point-slope equation:

$y - y_1 = m(x - x_1)$

anonymous · Answer

Thanks! Fastest responses I've ever received lol XD

mathstudent55 · Answer

In your case, you are given $slope = m = - \dfrac{2}{5} $, and point $(-3, -5)$. 

Just substitute these values into the equation above.
Keep in mind that you need to subtract the x-coordinate and the y-coordinate of the point. Both your x- and y-coordinates are negative, so be careful with the signs.

mathstudent55 · Answer

@MrNood 

You wrote

"you know the 'point slope' form is 

y=mx+b" ...

That is actually the slope-intercept form, not  the point-slope form.

mrnood · Answer

soz - yes .

I'll read the question properly next time! :-)

anonymous · Answer

So, the answer would be y - 5 = -2/5 (x - 3)?

mathstudent55 · Answer

No. That is not the answer.
You did plug int he slope correctly, but above I mentioned that the coordinates of the point are both negative numbers and you need to be careful because you are subtracting two negative numbers.

mathstudent55 · Answer

Always start with the equation or formula.
Write it down. It will help you with the problem, but it will also help you memorize the formula or equation.

mathstudent55 · Answer

We start with the point-slope equation:

$y-y_1=m(x-x_1) $

Now we replace $x_1$ with -3, 
$y_1$ with -5,
and m with $- \dfrac{2}{5} $

$y-(-5)=-\dfrac{2}{5}(x-(-3)) $

Notice that all I did was the substitutions for x1, y1 and m.

Now simplify the subtractions of negative numbers.
Remember that subtracting a negative number is adding.

$y +5=-\dfrac{2}{5}(x+3) $

anonymous · Answer

OOoohhhhh. Okie. I see it now...>XD