A= sin ²15 + sin ²30 + sin ²45+ sin ²60+sin ²75 B= cos ²12+cos ²23+cos ²34+cos45+cos ²56+cos ²67+cos78

0 bình luận về “A= sin ²15 + sin ²30 + sin ²45+ sin ²60+sin ²75 B= cos ²12+cos ²23+cos ²34+cos45+cos ²56+cos ²67+cos78”

1. Đáp án:

   A = $sin^{2}$15 + $sin^{2}$30 + $sin^{2}$45 + $sin^{2}$60 + $sin^{2}$75

   ⇒ A = $cos^{2}$75 + $cos^{2}$60 + $sin^{2}$45 + $sin^{2}$60 + $sin^{2}$75

   ⇒ A = 1 + 1 + $sin^{2}$45

   ⇒ A = 2,5

   B = $cos^{2}$12 + $cos^{2}$23 + $cos^{2}$34 + $cos^{}$45 + $cos^{2}$56 + $cos^{2}$67 + $cos^{}$78

   ⇒ B = $sin^{2}$78 + $sin^{2}$67 + $sin^{2}$56 + $cos^{}$45 + $cos^{2}$56 + $cos^{2}$67 + $cos^{}$78

   ⇒ B = $sin^{2}$78 + 1 + 1 + $cos^{}$45 + $cos^{}$78

   ⇒ B = 3,9

    

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