Question 611729
1-cos^2(x)*1-tan^2(x)=sin^2(x)-2sin^4(x)/ 1-sin^2(x) 
**
Starting with left side:
(1-cos^2x)(1-tan^2x)
=sin^2x(1-sin^2x/cos^2x)
=sin^2x[(cos^2x-sin^2x)/cos^2x]
=[sin^2x(1-sin^2x-sin^2x)]/(1-sin^2x)
=[sin^2x(1-2sin^2x)]/(1-sin^2x)
=sin^2x-2sin^4x)/(1-sin^2x)
verified:
left side=right side