Question

Упростить выражение:
cos2a -cosa *cos3a

Answer 1

$cos2 alpha -cos alpha *cos3 alpha =2cos^2 alpha -1-cos alpha *(4cos^3 alpha -3cos alpha )= \ =2cos^2 alpha -1-4cos^4 alpha -3cos^2 alpha =-cos^2 alpha-1-4cos^4alpha$