Well, my problem is not to finding k. I’ve confusion to recognize is it p.d.f or not.
If I try on this way,
f(-0.5) = k(0.75)
f(1) = 2k
I didn’t understand how the above info/working or else will show
f(x) < 0. So it could not be a p.d.f. (As my book’s answer.)