Math Is Fun Forum

ac88218

Member

Registered: 2012-08-05

Posts: 3

point-gradient form of a linear equation

hello,
Just wondering if anyone can help me out with this question my teacher set me, thanks
"Find the equation of a line with a gradient of -4 and an x-intercept of 5"
hope someone can help...

Bob

Administrator

Registered: 2010-06-20

Posts: 10,648

Re: point-gradient form of a linear equation

hi ac88218

just typing this up.  Stay on-line if you can.

Bob

---

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

Bob

Administrator

Registered: 2010-06-20

Posts: 10,648

Re: point-gradient form of a linear equation

The point gradient form looks like this:

You are told that m = -4 and that (5,0) is one point.  So

Bob

---

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

ac88218

Member

Registered: 2012-08-05

Posts: 3

Re: point-gradient form of a linear equation

Thanks,
I know the formula, I think I need to know how to find the y-intercept to keep going from here because I know how to do it with both intercepts,
if you could help me find out how that would be great

Bob

Administrator

Registered: 2010-06-20

Posts: 10,648

Re: point-gradient form of a linear equation

OK.

I did add some more to post 3 but I'll show you how to get the y intercept without knowing that equation.

As the gradient is minus 4, that will mean for every 1 you step left in the x direction, the y coordinate will go up by  4. 

So step back a few points like this:

(5,0)  ... (4,4) ... (3,8) ... (2,12) ... (1,16) ... (0,20)

So the y intercept is (0,20)

Bob

---

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

ac88218

Member

Registered: 2012-08-05

Posts: 3

Re: point-gradient form of a linear equation

thanks so much, didn't realise it was that easy