If sin α + cos α = 13, then sin 2 (π 4 - α) = () A. 118B. 1718C. 89D. 29

If sin α + cos α = 13, then sin 2 (π 4 - α) = () A. 118B. 1718C. 89D. 29

∵ sin α + cos α = 13, then 1 + 2Sin α cos α = 19, 2Sin α cos α = - 89.sin2 (π 4 - α) = (22cos α − 22sin α) 2 = 12 (1-2sin α cos α) = 12 (1 + 89) = 1718, so B