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STRAIGHT LINE GRAPHS y = mx + c

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**STRAIGHT LINE GRAPHS ALL are of the form y = mx +c**

m is the GRADIENT of the line c is the ‘y intercept’

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**STRAIGHT LINE GRAPHS We must to be able to DRAW THE GRAPHS**

FIND THE EQUATION FROM A GRAPH

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**STRAIGHT LINE GRAPHS DRAWING THE GRAPHS WE NEED TO IDENTIFY TWO POINTS**

POINT 1 IS THE y INTERCEPT POINT 2 IS FOUND BY SUBSTITUTING A VALUE FOR x INTO THE FUNCTION DRAWING THE GRAPHS

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**If we use the example y = 3x - 1**

STRAIGHT LINE GRAPHS If we use the example y = 3x - 1 The y intercept is -1 REMEMBER (y = mx + c) So point 1 is (0,-1) If we substitute x = 1 then y = 3 - 1 so y = 2 So point 2 is (1,2)

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**STRAIGHT LINE GRAPHS NOTE THE TWO POINTS CHOSEN**

THE FINISHED GRAPH LOOKS LIKE THIS NOTE THE TWO POINTS CHOSEN

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**NOW WE MUST LEARN HOW TO FIND AN EQUATION FROM A GRAPH**

STRAIGHT LINE GRAPHS NOW WE MUST LEARN HOW TO FIND AN EQUATION FROM A GRAPH

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**STRAIGHT LINE GRAPHS SO ‘C’ IS -4 IF WE USE THIS GRAPH**

WE CAN SEE THAT THE LINE CROSSES THE Y AXIS AT THE POINT (0,-4) SO ‘C’ IS -4

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STRAIGHT LINE GRAPHS The gradient (m) is defined as

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**STRAIGHT LINE GRAPHS We need to find m (the gradient)**

We need to find the change in y We need to find the change in x The change in y is 4 The change in x is 2

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**STRAIGHT LINE GRAPHS So m = 2 Since the gradient is defined as**

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**We know the equation of the line is**

STRAIGHT LINE GRAPHS STRAIGHT LINE GRAPHS As y = mx + c We know the equation of the line is y = 2x - 4

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**STRAIGHT LINE GRAPHS Click here to draw graphs**

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EXAMPLE 1 Write an equation of a line from a graph

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