✔ 最佳答案
8JANsec(π/7) sec(2π/7) sec(3π/7)= 1 / ( cos(π/7) cos(2π/7) cos(3π/7) )= - 1 / ( cos(π/7) cos(2π/7) cos(4π/7) )= - 2 sin(π/7) / ( 2 sin(π/7) cos(π/7) cos(2π/7) cos(4π/7) )= - 2 sin(π/7) / ( sin(2π/7) cos(2π/7) cos(4π/7) )= - 4 sin(π/7) / ( 2 sin(2π/7) cos(2π/7) cos(4π/7) )= - 4 sin(π/7) / ( sin(4π/7) cos(4π/7) )= - 8 sin(π/7) / ( 2 sin(4π/7) cos(4π/7) )= - 8 sin(π/7) / sin(8π/7) = 8
9JAN(1/3)x + (2/3)y = (1/2)(x + y)x = yThe least [two] positive value x + y = 1 + 1 = 2 and 2 + 2 = 4 .
2011-11-07 20:41:11 補充:
Corrections :
9JAN
( 1 / (3+1) )x + ( 2 / (2+3) )y= ( 1 / (2+1) ) (x + y)
x/4 + 2y/5 = (x + y)/3
15x + 24y = 20(x + y)
5x = 4y
So
x = 4k (where k is an integer)
y = 5k (where k is an integer)
The least [two] positive value x + y = 4 + 5 = 9 and 8 + 10 = 18.