Junior high school math problems, please help!

1. The midline on the waist of the known isosceles triangle divides the circumference of the triangle into two parts, 9cm and 15cm, and finds the waist length and the bottom edge length of the triangle.

Let half of the waist length be x and the bottom length be y

Two possibilities x+y=15 3x=9

or x+y=9 3x=15

Get x=3 y=12 or x=5 y=4

That is, the waist length is 6 and the base length is 12 or the waist length is 10 and the base length is 4, because the sum of the two sides of the triangle is greater than the third side, so the first possibility is not established in the is that the waist length is 10 and the base length is 4

Let the waist be x and the bottom be y, then x+x 2=9, y+x 2=15, or x+x 2=15, y+x 2=9. In the first case, x=6, y=12, the sum of the two waists is equal to the third side, which cannot form a triangle and is rounded. In the second case, x=10 and y=4 are solved.

So the waist is 10 and the bottom is 4.

Let the waist length x and the bottom edge length y, there are: x+x 2=9, x 2+y=15 or x 2+y=9, x+x 2=15, and the solution is x=10, y=4

The other set of solutions is x=6, y=12, 2x=y, rounded. So the waist length is 10, and the bottom edge is 4 long

Solution: (1) 90° 120° 150° (2) 0cm

180°-60°) 360°=3 (cm)3 180°-30°) 360°=15 4 (cm) I did this question, my memory is a little unclear, Xixi, it's better to ask the teacher, and I can listen to it again in class later.

It's not good not to review.

The angle of A rotation is 90 degrees, then 60 degrees, and then 120 degrees, and the degree of C rotation is 0 degrees, then 120 degrees, and then 120 degrees.

(1)90° 120° 150°

2) Take a as the center of the circle, ac as the radius, and the arc length of the circle with a central angle of 120 (root number 3) 2

With b as the center of the circle, bc as the radius, and the arc length of the circle with a central angle of 150, add up.

1/3> - (1/3 > 丨-3丨" -丨+3 and 1/3丨.

Belongs"0+0"Because the absolute value can only be non-negative, the sum of the two absolute values is equal to 0, and both absolute values must be 0....So x=3, y=2....3x+2y=13

The general score can be known丨b丨》丨a丨, but A > B, so B must be negative, and A can be positive or negative.

So a = 3 7 or -3 7, b = -9 20

No, both sides cannot be divided by x at the same time, because x can be 0, and dividing any number by 0 is meaningless.

False, because when x = 0, the original equation is true.

Wrong! Instead of subtracting three from both sides, use the shift term 3x-2x=-3+3x=0

Incorrect, 3x 2x should be divided by 3 or 2 on both sides at the same time to get x=3 2

The equation is not unsolved, but x=0;

3x 2x is shifted to obtain 3x-2x =0, i.e. x=0;

Move items first, 3x-2x=-3+3

In merging similar terms, x=0

Equation x = 0

Wangjia shares: (2a +1)-(a-1)=2a -a+2;

Li shares: (5a -3a-2) - (2a +1) - (2a -a + 2) = a -2a-5

So the Li family's money has: (a -2a-5)*m*. Do the math yourself.

Shares: Zhang(2a 2+1)Wang[(2a2+1)-(a-1)]Li [(5a 2-3a-2)-(2a 2+1)-(2a 2+1-a+1)]=5a 2-2a-5) then the Li family deserves (5a 2-2a-5)*18%*(1-80%)

Note 2a is squared.

Wangjia shares: (2a +1)-(a-1)=2a -a+2;

Li shares: (5a -3a-2) - (2a +1) - (2a -a + 2) = a -2a-5

The Lee family deserves: (a -2a-5) m 18% (1-20%)=