Question

use the appropriate substitution to solve the following dy/dx= sin(x+y)+cos(x+y)

Answer 1

assume X + Y is equal to t therefore 1 + DY by DX is equal to DT by DX

therefore DY by DX is equal to DT by DX -1 equation one becomes
DT by DX minus 1 is equal to sin t + cost therefore Dt by DX is equal to sin t + cost - 1

therefore DT divided by sint+ cost minus 1 is equal to DX

Call tant is equal v
integrate both sides to get the answer