find two possible values of p if the lines px-y+1=0 and 3x+y+1=0 intersect at 45 degrees
I am rusty but I will give it a go.
find two possible values of p if the lines px-y+1=0 and 3x+y+1=0 intersect at 45 degrees
px-y+1=0 y=px+1 gradient =p
this line makes an angle of atan(p) with the positive axis I'll call this $$\theta_1$$
3x+y+1=0 y=-3x-1 gradient = -3
this line makes an angle of atan(-3) with the positive axis I'll call this $$\theta_2$$
Now we want
$$\theta_1-\theta_2 = \pm \frac{\pi}{4}$$
You need to use the last formula, do you think you can try to take it from here :)