cos(A + π/4) = 3/5
cosAcos(π/4) - sinAsin(π/4) = 3/5
(1/√2)(cosA - sinA) = 3/5
(cosA - sinA)² = (3√2/5)²
cos²A + sin²A - 2sinAcosA = 18/25
1 - sin2A = 18/25
sin2A = 7/25