Question

докажите торжество sin⁴a-sin²=cos⁴a-cos²

Answer 1

$sin^4 alpha -sin^2 alpha =sin^2 alpha (sin^2 alpha-1)=-sin^2 alpha cos^2 alpha \ cos^4 alpha -cos^2 alpha =cos^2 alpha (cos^2 alpha -1)=-sin^2 alpha cos^2 alpha$