Given that the image of a function passes through both points (1,2) and (- 1,8) 1, find the analytic expression. 2. Judge whether the point (2, - 1) is on the analytic expression of the function

Given that the image of a function passes through both points (1,2) and (- 1,8) 1, find the analytic expression. 2. Judge whether the point (2, - 1) is on the analytic expression of the function

The analytic formula of a function is y = KX + B
X = 1, y = 2; X = - 1, y = 8
We get {2 = K + B}
8=-k+b
∴﹛k=-3,b=5
The analytic expression of a linear function is y = - 3x + 5
When x = 2, y = - 6 + 5 = - 1
(2, - 1) on the function image