PP-T2-DS90

[emmaaqua]

What is the value of a4 - b4 ?

(1) a2 - b2 = 16

(2) a + b = 8

Ans:C

這題好像不難..但我就是不會算...
請幫忙解惑一下~謝謝~

[amazingslim]

a4 - b4=(a2+b2)(a2-b2)=(a2+b2)(a+b)(a-b)

(1)a2 - b2 = 16
不知道a2+b2

(2)a+b=8
不知道a2+b2，a-b

combine(1)(2)
可得出a-b=2
so a=5,b=3

[emmaaqua]

瞭解~!謝謝amazingslim清楚的答覆嚕~