Find the monotone interval of function y = 3sin (2x + π / 4) y = 1 + SiNx y = - cosx is not a number of sine cosine, regardless of the numbers and signs in front of it I want to know why

Find the monotone interval of function y = 3sin (2x + π / 4) y = 1 + SiNx y = - cosx is not a number of sine cosine, regardless of the numbers and signs in front of it I want to know why


Y = 3sin (2x + π / 4) let a = 2x + π / 4 have an increasing interval: a [2K π - π / 2,2k π + π / 2] namely: 2x + π / 4 [2K π - π / 2,2k π + π / 2] 2x [2K π - 3 π / 4,2k π + π / 4] x [K π - 3 π / 8, K π + π / 8] y = 1 + SiNx y = - cosx