Does stationary waves a straight wave means cancels out each other ?

Dear student

The standing waves CAN cancel each other, but they must be exactly out of phase and of the same amplitude and frequency on a continuing basis. Creating this situation is the hard part. Imagine waves exactly parallel to each other, but exactly out of phase

Good Luck 

They do cancel each other when the peaks of one coincide with the troughs of the other, but since they move in opposite directions, this only happens at specific moments in time (every half period). At other moments (one fourth period later), the peaks of both waves will coincide (and so will their troughs).