PP-T1-DS137

[smilego]

137. 14062-!-item-!-187;#058&009802
If x is an integer, is (x2 + 1)(x + 5) an even number?

(1) x is an odd number.
(2) Each prime factor of x2 is greater than 7.

請問第2個答案,要怎麼推出呢??謝謝

[小花]

If x is an integer, is (x^2 + 1)(x + 5) an even number?

(1) x is an odd number.
(2) Each prime factor of x^2 is greater than 7.
所有質數只有2是偶數 質數大於7 代表每個質數因數必是奇數
竒*奇=奇 (x^2 + 1)(x + 5)
(奇+1)=偶數
偶*偶=偶 偶*奇=偶

[smilego]

懂了, 謝謝!! :)