Gold medal, one class, one math exercise (try this eighth grade, the second semester of the next eighth grade), P 164, the answer to question 24 (I will type if there is no problem).

Solution: (1)? B= 90？ , cut along the neutral line EF, or AB=AC, cut along the height AD.

⑵ AB=2BC, cut along the midline EF, or? C= 90？ , ? A= 30？ , cut along the midline.

⑶ ? B= 90？ , AB=2BC, cut along the midline, or AB=AC,? BAC= 90？ Cut along the height AD. (4) Take a small D on the side of BC and make it? GDB=？ B intersects AB at G, the midpoint E of AC intersects BC at F with EF‖GD, and EF is the shear line (omitted).

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