Persamaan garis lurus yang saling tegak lurus merupakan persamaan garis lurus yang saling berpotongan secara tegak lurus satu sama lain. Hal ini berarti sudut yang terbentuk adalah sudut siku-siku atau [img width=24,height=22]data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAABgAAAAWCAMAAADto6y6AAAAAXNSR0IArs4c6QAAAGBQTFRFAAAAAAAAAAA6ADpmADqQAGa2OgAAOgA6OjqQOmaQOpDbZgAAZjoAZpDbZrbbZrb/kDoAkDo6kNv/tmYAtmY6tpA6ttv/25A625Bm27Zm2////7Zm/9uQ/9u2//+2///b/IKN6QAAAAF0Uk5TAEDm2GYAAAAJcEhZcwAADsQAAA7EAZUrDhsAAAAZdEVYdFNvZnR3YXJlAE1pY3Jvc29mdCBPZmZpY2V/7TVxAAAAiklEQVQoU8VQ0RKCMAzLqpsiOFDUwZjs///SlrK7vfpEXpol7dIrcCjyyxjyssLslEyO7lzGc8RMTyA5j8AkXWN+cLmwloebdqytxcI89GpgtGqKu09wT8S3s9y8GyUjdYaaoTaqW6xtv32vQRWCPEXToIL8lm2xGK97FwRqPhufnDlV+qFn/zf8BxHHCCC0Z5izAAAAAElFTkSuQmCC[/img]. Hasil kali gradien dari dua garis lurus yang saling tegak lurus adalah -1.[br][center][img width=101,height=22]data:image/png;base64,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[/img][/center] Contoh persamaan garis lurus yang saling tegak lurus adalah persamaan garis  [img width=88,height=22]data:image/png;base64,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[/img] dan [img width=77,height=30]data:image/png;base64,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[/img]. Hal ini dibuktikan dengan sudut yang dibentuk pada perpotongan kedua garis tersebut adalah sudut siku-siku.[br][br]Pembuktian:[br][img width=101,height=22]data:image/png;base64,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[/img][br][img width=90,height=39]data:image/png;base64,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[/img][br][img width=140,height=22]data:image/png;base64,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[/img]