求救....數學~幫幫手.....

K.Y~勤

1.The common difference ｄ of an arithmetic sequence is 3. The 10th term is 23. Find the first term.

2.Solve the equation 2sin^2 χ + cos^2 χ=1 where 0o<θ<360o

3.630o =

A. 1.75 radians
B. 1.75πradians
C. 3.5radians
D. 3.5πradians

4. For the airthmetic series 7+15+...+159, find
(a) the number of terms η
(b) the 7th term T(7)
(c) the sum of the series S(n)

唔該大家.....會加分的

去完廁所唔洸手

1. a + (10-1)3 = 23
                    a =-4
2   2sin^2 (x) + cos^2(x) = sin^2(x) + cos^2(x)
                          sin^2 (x) = 0
                                   x = 0,180,360
3.D
4a 20
  b 7 + (7-1)8 = 55
  c (7+159)/2 X 20 = 1660