Докажите тожество 8б

Question

Докажите тожество 8б

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Answer 1

Sin^4a - sin^2a = cos^4a - cos^2a = sin^2a(sin^2a - 1) = cos^2a(cos^2a - 1) = 
sin^2a*-cos^2a = cos^2a *-sin^2a

Answer 2

(sin^4a-cos^4a)-(sin²a-cos²a)=0
(sin²a-cos²a)(sin²a+cos²a)-(sin²a-cos²a)=0
(sin²a-cos²a)*1-(sin²a-cos²a)=0
sin²a-cos²a-sin²a+cos²a=0
0=0