Solving mathematical problems! The process of solving problems is required 1. Given that CD is the middle line of triangle ABC, BC = 10cm, AC = 7cm, what is the perimeter difference between triangle BCD and triangle ACD? 2. The perimeter of an isosceles triangle is 25cm. The median line on one waist divides the perimeter into two parts: 3:2? 3. If one internal angle of an isosceles triangle is 80 degrees, then the degrees of the other two internal angles are -? 4. In the triangle ABC, if the angle a is 90 degrees, BD is the bisector of the angle, De is perpendicular to BC and E is the midpoint of BC, then the angle ABC is equal to -? 5. The length of the base of an isosceles triangle is 5cm. If the difference between the two parts is 3cm, the waist length is -? How many significant numbers are there in the approximate number of 24000, accurate to - digits? 7. The 1998 power of minus 2 times its 1999 power equals? 8. Given that the lengths of three sides of a triangle are 14, 4x and 3x respectively, the value range of X is -? 9. For a piece of land with a triangle (acute angle or right angle), it is required to draw a line segment through a certain vertex of the triangle and divide its area into two parts equally. How do you think this line segment should be drawn? How much is the 2005 power of 10.2 multiplied by the 2006 power of 0.5?

Solving mathematical problems! The process of solving problems is required 1. Given that CD is the middle line of triangle ABC, BC = 10cm, AC = 7cm, what is the perimeter difference between triangle BCD and triangle ACD? 2. The perimeter of an isosceles triangle is 25cm. The median line on one waist divides the perimeter into two parts: 3:2? 3. If one internal angle of an isosceles triangle is 80 degrees, then the degrees of the other two internal angles are -? 4. In the triangle ABC, if the angle a is 90 degrees, BD is the bisector of the angle, De is perpendicular to BC and E is the midpoint of BC, then the angle ABC is equal to -? 5. The length of the base of an isosceles triangle is 5cm. If the difference between the two parts is 3cm, the waist length is -? How many significant numbers are there in the approximate number of 24000, accurate to - digits? 7. The 1998 power of minus 2 times its 1999 power equals? 8. Given that the lengths of three sides of a triangle are 14, 4x and 3x respectively, the value range of X is -? 9. For a piece of land with a triangle (acute angle or right angle), it is required to draw a line segment through a certain vertex of the triangle and divide its area into two parts equally. How do you think this line segment should be drawn? How much is the 2005 power of 10.2 multiplied by the 2006 power of 0.5?

Analysis:
1. ∵ CD is the middle line, ad = BD
∴（BC+BD+CD)-(AC+AD+CD)=BC-AC=10-7=3
2. If waist length = m, then bottom length = 25-2m
(M + m / 2) / (M / 2 + 25-2m) = 3 / 2 or 2 / 3
The solution is m = 10 or M = 20 / 3
Bottom length = 5, or 35 / 3
3. If the top angle is 80 degrees, the two bottom angles are equal and equal to 50 degrees
If the base angle is 80 degrees, the other base angle is 80 degrees and the top angle is 20 degrees
4. Obviously, if AB = be = BC / 2, angle c = 30 degrees, then angle B = 60 degrees
5. Let waist length = m, then M + m / 2 = 5 + m / 2 + 3, M = 8
When m + m / 2 + 3 = 5 + m / 2, M = 2, and 2,2,5 are not triangles,
6. Two, to the nearest thousand
7、（-2）^1998*(-2)^1999=(-2)^3997
=-2^3997
8. 4x-3x ＜ 14 ＜ 4x + 3x, 2 ＜ x ＜ 14
9. Take the midpoint of any side and connect the midpoint with the corresponding vertex
10、2^2005*(0.5)^2006
=2^2005*(0.5)^2005*0.5
=(2*0.5)^2005*0.5
=1^2005*0.5
=1*0.5=0.5
Ha ha, there are too many questions to finish