Math Is Fun Forum

jxharmon

Member

Registered: 2007-01-08

Posts: 104

y-intercept please check

find the y-intercept    -7x-y=7;  -y=7x+7 my choices are  A.(-1,0)  B.(0,-7) C.(-7,0) D. (0,-1)
my thinking is B correct??

mathsyperson

Moderator

Registered: 2005-06-22

Posts: 4,900

Re: y-intercept please check

Your thinking is right. To find the y-intercept, you need to rearrange the equation to make y the subject and then look at the constant term. In this case:

-7x-y = 7
-7x = 7+y
y= -7x -7

The x co-ordinate of the y-intercept is always 0, so you can instantly tell that two of those options are wrong.

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Why did the vector cross the road?
It wanted to be normal.

pi man

Member

Registered: 2006-07-06

Posts: 251

Re: y-intercept please check

Another way to think about it is to remember what the definition of Y intercept is.   It is the value of Y when X=0.   Substitute 0 for x in your original equation and you'll find Y=-7.