please help me solve:
(1-cos^3ө)/(1-cosө) - cos^2ө-1
did you notice the difference of cubes ?
(1-cos^3ө)/(1-cosө) - cos^2ө-1
=(1 - cosө)(1+ cosө + cos^2ө)/(1 - cosө)- cos^2ө-1
= 1+ cosө + cos^2ө - cos^2ө-1
= cosө
(1-cos^3ө)/(1-cosө) - cos^2ө-1
(1-cos^3ө)/(1-cosө) - cos^2ө-1
=(1 - cosө)(1+ cosө + cos^2ө)/(1 - cosө)- cos^2ө-1
= 1+ cosө + cos^2ө - cos^2ө-1
= cosө