If an equations has y and/or x but no higher power (eg x², X³) then it's a straight line equation
Vertical and horizontal lines
x=a is a vertical line crossing a on the x-axis
y=a is a horizontal line through a on the y-axis
gradient
gradient of a line is how steep it is the larger the gradient the steeper the slope
a negative gradient means the slope is downhill
to find the gradient
change in y
_________________
change in x
Example
Point a = (6,50) and point b = (1,10)
the change in y = 50 - 10 = 40
the change in x = 6-1 = 5
gradient = 40/5 = 8
y = mx + c
m = gradient of line
c= y intercept
Example
equation of this line is y = 1/2 x + 15
Example 2
If you're given two points and on a line you can find the gradient and then you can use the gradient and one of the points to find the equation of the line
QUESTION: Find the equation of the straight line that passes through (-2,9) and (3,-1
M = change in y
__________
change in x
which is
-1 - 9
__________
3 - -2
which is
-10
____________
5
which is -2
substitute one of the points into the question you just found (eg (-2,9)