Consider two pairs of parallel lines, one pair horizontally and another is inclined from vertical position. If one of the four angles is given, then the other three angles can be easily identified. First select the angle which is down to the known angle, it will be same as first one. Then according to the law, that a straight lines consists of 180 degrees. For example if the known angle is 114 degrees, the unknown angle will be 180-114= 56 degrees.
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