P 18- 13
& ltC = & ltD = & ltb DB//CE & lt； DMF = & ltENF (two straight lines are parallel and have the same angle)
14 draw a parallel line c, and then make a height.
The problem 15 is proved by 123: all triangle AFD are equal to triangle BEC.
Because AD=CD, AE=CF
Because AF=EC
Angle B= angle d, so triangle AFD is equal to triangle BEC.
P 19 Question 9 chooses the angle abc, because AB=AC, and the angle ABC is an isosceles triangle.
20 or 22 20 65 205 and root 7 DDBD
There are three P20- 10, and the figure is omitted.
-sketch 1 1
The square of-126 plus the square of 8 equals 100, the root number 100 equals 10, 10 plus 6 equals 16,
-13 (1) AC is male * * * side, < FAC = & ltCAE, & ltCEA = & ltAFC {& ltFAC = & ltCAE, AC=CA, & ltCEA = & ltAFC, so EC = cf
{CE=CF，& ltCEB = & lt； CFD, CB=CD, so triangle BCE is equal to triangle CDF(HL).
(2) Root number 34
P21DBBCBDCB 30 Sphere 4 -2 36cm2 4 species
P22 - 13 3×4÷2×2= 12
4×2+2×3= 14
2×5= 10
10+ 14+ 12=36
P23 Sampling survey of brominated diphenyl ethers 9 544.5 20 2
P24— 10( 1) Cheng: (98+80+80)/3=86 Yang: (95+93+90)/3=92.6.
Lin: (80+100+100)/3 = 93.3 champion, runner-up Li Yang, runner-up.
(2) Li Cheng: 78.24 Li Yang 93.2 Lin Fei: 92 champion Li Yang, Asia: Lin Fei, season: Li Cheng.
Average A 1.69m, B 1.68m stability s2a0.0006s2b0.0001315ab.
P25ddd > > < >-2 ≤ t ≤ 8x
p26- 10 6(2x- 1)-24≤4( 1+x)
12x-6-24≤4+4x
12x-30≤4+4x
8x≤34
X≤ 17/4
-1 1 Let the original prices of A and B be A and B respectively, and the original price of B < a & lt2b (1).
After adjusting the price of 10%, the new prices of A and B are 1. 1a (as m), 1 b (as n), and the formula (1) is multiplied by/kloc-. 1. 1a & lt； 2.2b, namely n
Add 10 yuan, and the new prices of A and B are a+ 10 (as m), b+ 10 (as n) and (1) respectively. Add 10 to get B+10 < 2b+ 10, where 2n is 2b+20, obviously 2b+ 10.
N<m & lt2n, so this price adjustment scheme is still less than twice.
12. design: total capital of x yuan.
15% x+ 10%(x+ 15% x)÷30% x-700
0. 15x+0. 1x+0.0 15x〈0.3x-700
x÷20000
Therefore, when the merchants invest more than 20,000 yuan, they can choose to sell at the end of the month, so as to get more profits.
13( 1) has X flower beds A and Y flower beds B. In order to ensure enough roses and azaleas, then
50x+ 80y = 1250 ①
100x+90y = 1930 ②
The solution is y=8 (pieces) and x= 12 (pieces).
P27 CBBCBC a>0 b=0 -3 3, -2-100 root number 5,-100 northwest, 5km in 50 direction, a problem 2,1-1< a < 3 rt.
P28 - 15 2×7÷2=7
5×5=25
2×5÷2=5
2×5÷2=5
5+5+25+7=42 square centimeters
-16 select the coordinate point b, and don't forget the arrow, A( 1, root number 3) b (0,0) c (2,0).
— 17(2)B(-3，-3) C'(- 1，0)
P29 square of dbbbd v π r, h π v, r, h y= y=2x+4 y 1 greater than y2 y=6x x=-6 y=-9.
P30— 12 If the proportional function Y = kx. 2 = K *(2), then K=- 1. Analytical formula y =-X.
The linear function (-X)/X+2=(4-Y)/(Y-2) is arranged as follows: Y=X+4.
The area of the triangle PQO is 2*4/2=4.
13 question 34 =22k+b
36+23k+b
2- 1: k=2
From 1: b=- 10.
So y=2x- 10.
The third question: when y=30, x=20.
So the length of the shoes is 20 cm.
14( 1)y 1+xy2 = 12+0.4x。
(2) A: Xiao Bin chose to rent a disc for bookkeeping.
P3 1 DBADCD x≥3 1，2，3 16， 15.8， 16。 40 meters ≥0
p32— 12 { 3x-2 & lt； 4x {-x & lt； 2
{3-5 times & gt3x-5 {x <; 1
-2 & lt； X< 1 integer solution. 0.- 1
- 13
- 14( 1) 10x+8( 15-x)≤ 144 6x+8( 15+x)≤ 102
(2)*** There are four schemes: gift box A 9 and gift box B 6.
Or gift box a will arrange 10 boxes, and gift box b will arrange 5 boxes.
Or a gift box 1 1 box, and a gift box with 4 boxes.
Or arrange 12 boxes for gift box a and 3 boxes for gift box B.
- 15 ( 1)A(6，0)B(0，6)
(2){4=k+b 0=4k+b
2- 1: k=-2
b=8
Y=-2x+8(x is not equal to 4_)
(3)S=X(8-2X)/2 has no solution.