Упростить 8cos^4(a)-8cos^2(a)-cos4(a)

Question

Упростить 8cos^4(a)-8cos^2(a)-cos4(a)

Answer 1

8cos^4(a)-8cos^2(a)-cos4(a)  = 8cos^4(a)-8cos^2(a)-2(2cos^2a-1)^2)+1=

 

=8cos^4(a)-8cos^2(a)-8cos^4a-2+8cos^2a+1=-1