The values given in the table are :
x y
1 1
2 -1
3 -3
4 -5
The coordinates are : (1,1) ,(2,-1) , (3,-3) and (4,-5)
The formular for equation of a linear function is given as:
y=mx +b
where m is the gradient of the line and b is the y - intercept
The slope m is given by the formula;
m=change is y-coordinates/change in x-coordinates
Taking points (1,1) and (4,-5) the slope will be:
m= (-5-1)/ (4-1)
m= (-6)/(3)
m= -2
Then apply the formula for slope to find the y intercept b
m= change in y values/ change in x values
Taking m =-2 , the point (1,1) and an imaginary point on the line, (x,y) then it will be;
-2 = y-1 / x-1 ----------multiply both sides of equation by (x-1)
-2 ( x-1 ) = y-1 -------- open brackets on the left side of equation
-2x +1 = y-1 ---------collect like terms as;