SOLUTION: I need to find the exact value of this expression {{{ 1-cos^2 (20 degrees)-cos^2 (70 degrees)}}} using fundamental identities or the Complementary Angle Theorem. I thought maybe th

Question 281505: I need to find the exact value of this expression using fundamental identities or the Complementary Angle Theorem. I thought maybe the Complementary Angle Theorem would help but I am not sure how. Thank you for any help. :) By the way, both cosines are squared but when I preview, it does not look like they show up.
Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
I need to find the exact value of this expression using fundamental identities or the Complementary Angle Theorem. I thought maybe the Complementary Angle Theorem would help but I am not sure how. Thank you for any help. :) By the way, both cosines are squared but when I preview, it does not look like they show up.
-------------------------
(1 - cos^2(20)) - cos^2(70)
=====
Note: 1-cos^2(2) = sin^2(2)
=====
= sin^2(20) - cos^2(70)
=====
Note: sin(20) = cos(70)
=====
= cos^2(70) - cos^2(70)
= 0
===============================
Cheers,
Stan H.
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