As shown in the triangle ABC, ad is perpendicular to D under the following conditions: (1) angle B + angle DAC = 90 degrees, (2) angle B = angle DAC, (3) CD of ad = AC of AB, (4) The square of AB = BD times BC, where it is certain to determine that the triangle ABC is a right triangle, there are choices a, 1 B, 2 C, 3 D, 4

As shown in the triangle ABC, ad is perpendicular to D under the following conditions: (1) angle B + angle DAC = 90 degrees, (2) angle B = angle DAC, (3) CD of ad = AC of AB, (4) The square of AB = BD times BC, where it is certain to determine that the triangle ABC is a right triangle, there are choices a, 1 B, 2 C, 3 D, 4

1) No, ∵ ad ⊥ BC, ∵ B + ⊥ bad = 90 °, ∵ B + ⊥ DAC = 90 °, ∵ bad = ≁ DAC, ≁ it is impossible to prove that △ ABC is a right triangle; (2) Yes, ∵ B = ≁ DAC, then ∵ bad = ∨ C, ∫ B + ∨ bad = ∨ C + ∨ DAC = 180 ° △ 2 = 90 °; (3) can ∵ CD: ad = AC: AB, ∨ RT △ abd ∽ RT