Imagine 🔺️ABD has been sheared, A || to BD, from where <ACB=<ACD=90° and 🔺️s ACB & ACD are congruent, so 🔺️ACD has been sheared 2× as far as 🔺️ACB, so <CAD is less than <BAC (which is 10°). So <BAD must be less than 20°.
Imagine 🔺️ABD has been sheared, A || to BD, from where <ACB=<ACD=90° and 🔺️s ACB & ACD are congruent, so 🔺️ACD has been sheared 2× as far as 🔺️ACB, so <CAD is less than <BAC (which is 10°). So <BAD must be less than 20°.