(1) The straight line passes through the origin, and the intercept on the two coordinate axes is 0. Let the linear equation be y=kx, and bring in the data of point P, it is easy to get that the linear equation is y = (-5/4) x.

(2) The straight line does not pass through the origin. Let the linear equation be y=kx+b, the intercept on the X-axis is |-b/k|, and the intercept on the Y-axis is |b|, then the equation |-b/k|=|b| can be obtained, and then the coordinates of point P are brought into 4k+b=-5 of the equation to solve the simultaneous equations.

K= 1, b=-9 or k=- 1, and b=-4. Then two straight lines meet the conditions, y=x-9 or y=-x-4.