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(i) Take y2 = 2cos(x) (the same as y1)
(ii) Take y2 = -2cos(x) (opposite to y1)
(iii) Regarding k1, k2, I do not understand their meaning,
since they are not defined in the post - and, therefore, can not answer.
In part (iii), your post does not look like as a Math problem.
In whole, the problem in (i) and in (ii) is as if you want to ask,
how many is 1 + 1, or how many is 1 - 1, dressing it up in different smart words.