CBDBCCBBD obtuse angle 12 2 3 6 is not acceptable.

9.( 1)△ACD△ACE△BCE△CDE(2)△CBD△ABC

1. 1(2)

CABCBDCBC 25 4 14

8.97.5 9. 15 10. 15

1.2( 1)

DADACBABD does not belong to 2. A triangle is equilateral.

7. Is it 8? If two numbers are opposite, then the sum of the two numbers is zero.

9. If a number is a complex number, its absolute value is its reciprocal.

1.2(2)

AADDABABC's force line segment is correct. 7. For example, x=-3.

8. ∫ ad//BC ∴∠ b = ∠ c = ∠ c ∠∠ EAD = ∠ DAC ∴∴∴ ad bisects the external angle of △ABC ∠EAC.

This is a true proposition.

9. True proposition. Reason:

x^2-4x+7=x^2-4x+4+3=(x-2)^2+3

∴ (x-c) 2+3 ≥ 3 ∴ x 2-4x+7 is not less than 3.

Pure hands! Hope to adopt