The following information about a certain function is provided: For a function, the following information is provided: (1) Its image is a straight line (2) The line passes through three points (0,0), (1, - a), (a, - 4) (3) The value of function y decreases with the increase of independent variable x Find the expression of the function

The following information about a certain function is provided: For a function, the following information is provided: (1) Its image is a straight line (2) The line passes through three points (0,0), (1, - a), (a, - 4) (3) The value of function y decreases with the increase of independent variable x Find the expression of the function

Let the equation of the line be y = KX + B
Because the line through (0,0) into the equation has 0 = k * 0 + B, then B = 0, y = KX
And because the straight line passes through (1, - a), (a, - 4) and is brought into the equation, then
k=-a
If K ^ 2 = 4 is obtained from Ka = - 4 simultaneous equation, then k = 2 or K = - 2
Because y decreases with the increase of X, the function expression is y = - 2x