Verified Answer :

PR3D3T0R
  1. square both sides, a straight forward method. 
    2. hand plot 
    3. calculator plot, not recommended.Let Y=sin x + cos x -1 
    Y=0, find x=? 
    4. Substitute 1=sin^2(x) + cos^2(x) on the right hand side 
    Y1=sin^2(x) - sin(x) 
    Y2=cos^2(x) - cos(x) 
    Y1 + Y2=0, Y1=0, Y2=0, 
    a(a-1)=0, so, a=0, a=1, where a=sin(x), or cos(x), 
    so x=0, pi/2 
    Have a good day!

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