請大家幫幫我,教我 ....下列的數學我不懂做
1. The common difference D of an arithmetic sequence is 3. The 10th term is 23. Find the first term.
2. The sales of a magazine in the past 4 months were in a geometric sequence with common ratio 1.06. If the sales in the last month was $20000, Find the sale of first month.
3. Solve the aquation 2sinx² + cos²x =1 where 0∘< θ∘< 360∘.
4. 630∘=
a. 1.75 radians
b. 1.75π radians
c. 3.5 radians
d. 3.5π radians
我有的數學唔識做(help)請大家幫幫助..
2007-12-04 6:50 pm
回答 (2)
2007-12-04 8:42 pm
✔ 最佳答案
1. Let A = 1st termB = the Nth term
D = common difference
B = A +(N-1)D
N=10, B=23
23 = A +(9-1)*3
A = -4
The first term = -4
2. Let N=the nth term
R = common ration
N = AR^(n-1)
when n=3, R = 20000 (assume "the last month" = the month before month 4 i.e the
3rd month)
20000 = A(1.06)^(3-1)
A = 17800.0 (or 20000/1.1236)
The first term = 17800.0
3. {Assume the question shoudl be read as : 2(sinx)^2 + (cosx)^2 = 1}
2(sinx)^2 + (cosx)^2 = 1
2(sinx)^2 + {1-(sinx)^2} = 1
(sinx)^2) = 0
x = 2n(pi) n = 0, 1, 2, .....
Solution x = 2(pi) = 180 degree
4. 630 degree = 630*(2(pi))/360 rad
= 3.5*(pi) rad
Solution is (d)
2007-12-04 8:07 pm
第一題用 A.P.
第n 個term = A+(n-1)d
so 23=A+(10-1)x3
a=-4
第二題用G.P.
第N個TERM = a(d)^(n-1)
so 20000=a(1.06)^(3)
a=16792.386
第三題
先問sinx² 是否正確, 還是sin²x?
因為前著計算十分費時, 而且應該是a math 課程
第n 個term = A+(n-1)d
so 23=A+(10-1)x3
a=-4
第二題用G.P.
第N個TERM = a(d)^(n-1)
so 20000=a(1.06)^(3)
a=16792.386
第三題
先問sinx² 是否正確, 還是sin²x?
因為前著計算十分費時, 而且應該是a math 課程
收錄日期: 2021-04-16 16:25:12
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20071204000051KK00663