Equations Of Straight Lines - What Am I Doing Wrong?  TOPIC_SOLVED

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Equations Of Straight Lines - What Am I Doing Wrong?

Postby Dockers_Girl on Sat Feb 26, 2011 11:16 am

find the eqaution of the straight line with the gradient 0.5 and passing through the point (3, 4)

m = 0.5
x = -1
y = 10

y=mx+b
(-10) = (0.5)(-1) + b
-10 = -0.5 + b
b = -9.5

therefore my answer would be y = 0.5x - 9.5
but the answer is y = -4x-1
Last edited by Dockers_Girl on Sat Feb 26, 2011 12:24 pm, edited 1 time in total.
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Postby stapel_eliz on Sat Feb 26, 2011 12:19 pm

Dockers_Girl wrote:find the eqaution of the straight line with the gradient 0.5 and passing through the point (3, 4)

m = 0.5
x = -1
y = 10

The point you are given is "x = 3, y = 4". Where did "x = -1, y = 10" come from? :confused:

Dockers_Girl wrote:b)through (2,5) and (6,9)

my working out:

-1-9/0-2 = -10/-2 = -5

It looks as though you are using the points (0, -1) and (2, 9)...?

Instead, try plugging the given points, (2, 5) and (6, 9), into the slope formula:

. . . . .

Simplify to get the value of the slope (or "gradient"). Then pick either one of the given points and plug it, along with the slope, into one of the formulas for a straight line.

Simplify, and solve for "y=" to get the answer. :wink:
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