✔ 最佳答案
1.(a) f (2a) = 6 - 2(2a)² = 6 - 2(4a²) = 6 - 8a²
(b) f ( a + 2 ) = 6 - 2(a+2)² = 6 - 2(a² + 4a + 4)
= 6 - 2a² - 8a - 8
= -2a² - 8a - 2
2. 2 f (2) - f (3) = 5
2 [(2)² + k(2) - 2] - (3²) +3 k - 2) = 5
2(4 + 2k - 2) - (9 + 3k - 2)= 5
2 (2 + 2k) - (7 + 3k) = 5
4 + 4k - 7 - 3k = 5
k - 3 = 5
k = 8
其實做 f ( x ) 這類數,只要將 f (?) 的 (?) 代入條式到就做到嫁啦!
e.g f ( x ) = 5x + 3,求 f ( x + 2 )
首先將 f( x + 2 ) 的 ( x + 2 ) 代入 5x + 3 的 x 到就得啦!
f ( x + 2 ) = 5(x + 2) + 3
= 5x + 10 + 3
= 5x + 13