✔ 最佳答案
1)let x be one number. Then 12-x is the other number :
x(12 - x)
= - x^2 + 12x
= - (x^2 - 2(6)x + 6^2) + 6^2
= - (x - 6)^2 + 36
when x = 6 , x(12-x) have the maximum value of 6(12-6) = 36
The two numbers both are 6 and (12-6) = 6 .
2)let x be one number. Then 40-x is the pther number :
x(40 - x)
= - x^2 + 40x
= - (x^2 - 2(20)x + 20^2) + 20^2
= - (x - 20)^2 + 400
when x = 20 , x(40-x) have the maximum value of 20(40-20) = 400
The two number both are 20 and (40-20) = 20.
2009-12-16 22:02:17 補充：
- x^2 + 12x
= - (x^2 - 12x)
= - (x^2 - 2(6)x)
= - (x^2 - 2(6)x + 6^2 - 6^2)
= - (x^2 - 2(6)x + 6^2) + 6^2
= ........................
