※ 引述《skylion (溫暖的傳說)》之銘言：
: SinA+SinB=1
: CosA+CosB=0
: 求Cos平方A+Cos平方B
: 謝謝~
cosA = -cosB
1 - [sinA]^2 = 1 - [sinB]^2
=> 0 = [sinA + sinB][sinA - sinB]
= sinA - sinB
=> sinA = sinB = 1/2
[cosA]^2 + [cosB]^2 = 1 - [sinA]^2 + 1 - [sinB]^2
= 2 - 1/4 - 1/4
= 3/2
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