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Zhejiang education printing plate seventh grade second volume mathematics exercise book second volume. Chapter 1 1. 1 Understand all the answers of triangle (2).
1.∠C=80 2。 D=∠E=75 3 .∠ ADC = 80 3。 Acute angle 2 right angle 3 obtuse angle 1 4. Solution:

∠∠C = Rt∞, that is ∠ C = 90,

∠B=∠C/4

∴∠B=90 /4=22.5

∴∠a= 180-∠b-∠c = 180-22.5-90

∠A=67.5