Question

sin4平方-cos4平方+2cos平方)乘以tana乘以cota等于一求证

Answer 1

(sin^4 α-cos^4 α+2cos^2 α)*tanα*cotα

=[(sin^2 α+cos^2 α))(sin^2 α-cos^2 α)+2cos^2 α]*[tanα*(1/tanα)]

=[1*(sin^2 α-cos^2 α)+2cos^2 α]*1

=sin^2 α-cos^2 α+2cos^2 α

=sin^2 α+cos^2 α

=1