证明cosA四次方-sinA四次方=cosA平方(1-tanA)(1+tanA)_数学解答

证明cosA四次方-sinA四次方=cosA平方(1-tanA)(1+tanA)

人气：247 ℃　时间：2020-04-07 18:54:28

解答

cos^4(A)-sin^4(A)=[cos^2(A)+sin^2(A)][cos^2(A)-SIN^2(A)]
=1*[(cos^2(A)-sin^2(A)]
=cos^2(A)[1-sin^2(A)/cos^2(A)]
=cos^2(A) [ 1-tan^2(A)]
=cos^2(A)[(1+tanA)(1-tanA)]