(root number 5)/5, and the sine value of obtuse angle β is (root number 10)/ 10. According to the sine formula, sin(α-)=sinα*cosβ-cosα*sinβ.
Substitute the number, sin(α-β)=-7 times the root number 2/ 10.
(2): Similarly, according to sine sum formula and number, sin(α+β)= negative root sign 2/2.
Because acute angle α and obtuse angle β, α+β are located in the third quadrant, α+β=5π/4.