點計以下Formulas？（F.2數學）

2009-12-11 3:50 am

要ｓｔｅｐ。
Simplify the following.
1) (4a／2a^2－3a)＋(7a／3－2a)
2) [8x＋5y／(x－2y)^2]－(8／x－2y)

In the each of the following, make the letter in brackets the subject of the formula.
3) P＝2(ab＋bc＋ca) [b]
4) S＝n／2 [2a＋d(n－1)] [d]

5) The total surface area of a right circular cone is given by the formula
S＝兀r(r＋L), where r is the radius of the base circle and L is the slant height of the cone.

a) Make L the subject of the formula.
b) (i) If S = 314, r = 5 and L = 15,find the value of 兀.
(ii) If S = 264, r = 7 and 兀 = 22／7,find the value of L.

回答 (1)

用戶9112

2009-12-11 6:27 am

✔ 最佳答案

(1) 4a / (2a^2 - 3a) + 7a / (3 - 2a)
= 4a / [a(2a - 3)] - 7a / (2a - 3)
= (4 - 7a)/(2a - 3)
(2) (8x + 5y) / (x - 2y)^2 - 8 / (x - 2y)
= (8x + 5y) / (x - 2y)^2 - 8(x - 2y) / (x - 2y)^2
= (8x + 5y - 8x + 16y) / (x - 2y)^2
= 21y / (x - 2y)^2
(3) P = 2(ab + bc + ca)
P/2 = b(a + c) + ca
(P - 2ca)/2 = b(a + c)
b = (P - 2ca)/[2(a + c)]
(4) S = (n/2)[2a + d(n - 1)]
2S/n = 2a + d(n - 1)
2S/n - 2a = d(n - 1)
(2S - 2an)/n = d(n - 1)
d = 2(S - an) / [n(n - 1)]
(5)(a) S = πr(r + L)
S/πr = r + L
L = S/πr - r = (S - πr^2)/πr
(b)(i) 314 = π(5)(5 + 15)
π = 314/5/20 = 3.14
(ii) L = [264 - (22/7)(7^2)]/[(22/7)(7)]
L = (264 - 154)/22
L = 110/22 = 5

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點計以下Formulas？ （F.2數學）

回答 (1)

點計以下Formulas？（F.2數學）