F.1 數學方程式

w=10k+15/k-5 (w=75)
75=10k+15/k-5
75(k-5)=10k+15
75k-375=10k+15
75k-10k=15+375
65k=390
k=6

w=10k+15
75=10k+15
10k=15-75
10k=-60
10k/10=-60/10
k=-6

put w=75 into w=10k+15/k-5,

75=10k +15/k-5
75=10k^2 -5k +15
0=10k^2 -5k -60
k=2.71 or k= -2.21 (2d.p.)

bUt f.1 數應該無咁難:)
可能你打錯題目..? k-5 樓上的沒有加括號的.

而現在樓下的 : w=10k+15/(k-5), w=75
75=10k+15/(k-5)
75=10k(k-5) +15
0=10k^2 -50k -60
k=6 or k= -1

w = 10k+15/k-5 w=75
75 = 10k+15/k-5
75+5 = 10k+15/k
80 = 10k+15/k
80/10 = k+15/k
8 = k+k
8*15 = 2k
120 = 2k
120/2 = k
60 = k
k = 60