Question

Please help me simplify (1+tan^2y)(cos2y-1) Without using sec as the first part because i havent learned that yet. Do i FOIL it? or to I replace cos2y with one of the formulas?

Answer 1

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Answer 2

1+tan^2 y=1+sin^2 y/cos^2 y=(cos^2 y+sin^2 y)/cos^2 y=1/cos^y
And cos2y-1=cos^2y-sin^2y-(cos^2y+sin^2y)=-2sin^2y
then you can have a good conclusion.