[译] AB 与 AC 两线（垂直相交）形成的角称为直角。
[误] The angle contained by the lines AB and AC is a straight angle.

[正] The angle contained by the lines AB and AC is a right angle.
[注] 直角为 right angle，不是 straight angle。又如：A right angle is the angle between two perpendicular lines, i.e. an angle of 90°。直角是两条垂直线之间的角，即 90 度角。