Mathematics, how to do these two questions? How do you do math on these two questions

18.Solution: When x=2, 3(2-1)+4 2a=-13 3+8a=-13 8a=-16 a=-2 3(x-1)-8x=17 3x-3-8x=17

5x=20 x=-4

19.Solution: If there are x male students, then there are (x-20) female students x+(x-20)=8 45 2x=380 x=190 There are 190 male students and 190-20=170 female students.

Question 18: When x=2, 3(x-1)+4ax=(3+4a)x-3=2(3+4a)-3=12

3+4a=(12+3)/2=15/2

3+4a)x-3=15/2x-3=17

15/2x=20

x=40/15=8/3

Question 19: There are x girls and x + 20 boys.

x+x+20=45×8=360

2x=340

x=170x+20=190

There are 190 boys and 170 girls.

18.When x=2, 3+8a=-13 gives a=-23(x-1)-8x=17 x=-4

19.If there are x female classmates, then x+(x+20)=45 8 The solution is x=170 so x+20=190

There were 170 female students and 190 male students.

(1) According to the definition of ellipse|pf1|+|pf2|=2a=8

and pf1 vertical pf2, know |pf1|Squared +|pf2|Squared +|f1f2|squared = 36

2|pf1||pf2|=（|pf1|+|pf2|Squared +|pf1|Squared +|pf2|square = 64-36 = 28

pf1|-|pf2|Squared +|pf1|+|pf2|Square - 4|pf1||pf2|=64-56=8

pf1|-|pf2||= root number 8 = 2 root number 2

2) Set |pf1|=u angle f1pf2=w by |pf1|+|pf2|=2a=4 Know|pf2| =4-u

Then the area of the triangle pf1f2 = (1 2) u(4-u) sinw = (u+4-u+2)*(1 2)*(1 2)=3 2

The latter is the radius of the incut garden multiplied by half of the circumference, which is also the area of the triangle, so you can draw a picture yourself.

So u(4-u)sinw=3

cosw= [u 2+(4-u) 2-2 2] [2u(4-u)] = [u 2-4u+6] [u(4-u)]=6 [u(4-u)] 1

Let v= u(4-u) to get sinw=3 v cosw=6 v-1

1 = sinw squared + cosw squared = 9 v 2 + 36 v 2-12 v + 1 = 45 v 2-12 v + 1

So v=45 12=15 4

cosw=6/v-1=24/15-1=3/5

I see, the answer is 42 21 But, what is the question.

The definition of the odd function, f(-x) -f(x), is brought in. The constant is 0

(4) Solution: = - (root number 5 + 2 times root number 2) * (2 times root number 2 - root number 5) = - [(2 times root number 2) 2-(root number 5) 2] = - (8-5).

3 (5) solution = root number 36 - root number 49

Yuan Xiangfu style Zen feast potato = (Hee-2) 2-( 6) 2-(3-2+1 3).

4-6-1-1 3=-3 and 1 3

The first question plus sign is mentioned there is a root number 5 out, and the rest is very good; The second problem is the perfect square formula (a-b) 2=a 2-2ab+b 2

Question 1: Original = 5 ( 4 + 1) 5 * 9 - (6 3) = ( 4 + 1) 9 - 2

Question 2 (2-10) +40