19 question: y = 6x-3; 20 questions; X=-2 2 1 Question: 1.62
Question 22: COSB= one seventh a=7 b=8 COSB= one seventh is derived from cosine theorem.
Square of b = square of a+square of c-2cosb.
Square of 8 = square of 7+square of c -2 times 7 times c times one seventh.
That is, the square of c -2c- 15 =0 c=5, that is, AB=5.
Question 23: (1) because a(n+ 1 below) = half a(n below)
So an+1= half of an is a constant, which is a geometric series.
So an=a 1 time (half) n- 1 time =2 times twice 1-n times.
=2-n times of 2
(2)SS = a 1+A2+A3+A4+A5 = 2+ 1+ 1/2+ 1/4+ 1/8
= 0 in 365438+8.
24. Let the elliptic equation be: square x of Party A+square y of Party B =1.
From the square of a quarter of x-the square of y = 1, we can know that
Under the radical number c = 4+1= the radical number 5e of a = the radical number 5e = c = a, so a=3, so b = the square of a.
The square of -c =9-5=4
So the elliptic equation is the square of 9 x+the square of 4 y.