For what values of kkk does the equation sin(x)+cos(x)=k\sin(x) + \cos(x) = ksin(x)+cos(x)=k have solutions?
−2≤k≤2-2 \leq k \leq 2−2≤k≤2
∣k∣≤2|k| \leq \sqrt{2}∣k∣≤2
All real kkk
∣k∣≤1|k| \leq 1∣k∣≤1