F.4 maths

(1) 5-kx = 1/5kx

1/5kx = 8

(1/5x)k = 8

2k = 8

k = 3

(2) 3x+3 - 2(3x+2) = 30 - 3x

27(3x) - 18(3x) = 30 - 3x

10(3x) = 30

3x = 3

x = 1

1. 5^(-kx) = 8
(5^x)^(-k) = 8 (1)
Sub 5^x=0.5 into (1)
0.5^(-k) = 8
log [0.5^(-k)] = log 8
-k log 0.5 = log 8
-k = log 8 / log 0.5
-k = log (2^3) / log (2^-1)
-k = (3 log 2) / (- log 2)
-k = 3/-1
-k = -3
k = 3
2. 3^(x+3)-2(3^(X+2))=30-3^x
3^3 * 3^x - 2 * 3^2 * 3^x = 30 - 3^x
27(3^x) - 18(3^x) + 3^x = 30
10(3^x) = 30
3^x = 3
x = 1

1.
5-kx=8
(5x)-k=8
(0.5)–k=8
(0.5)–k=(0.5)-3
-k=-3
k=3

2.
3x+3-2(3x+2)=30-3x
3x+3-2(3x+2)=30-3x
27(3x)-18(3x)=30-3x
9(3x)+3x=30
10(3x)=30
3x=3
x=1

2009-10-25 18:15:23 補充：
慢了.....