sinα-cosα=(√2)/2
(sinα-cosα)^2=[(√2)/2]^2
(sinα)^2+(cosα)^2-2sinαcosα=1/2
1-2sinαcosα=1/2
2sinαcosα=1/2……………………………………(1)
(sinα+cosα)^2=(sinα)^2+(cosα)^2+2sinαcosα
(sinα+cosα)^2=1+2sinαcosα
將(1)代入,有：
(sinα+cosα)^2=1+(1/2)
(sinα+cosα)^2=3/2
sinα+cosα=±√(3/2)
考慮到α為銳角,舍去負(fù)值.
有：sinα+cosα=(√6)/2