document.write( "Question 415819: how to express cos(90-a) in simplest form \n" ); document.write( "

Algebra.Com's Answer #291443 by htmentor(1343) $\"\"$ $\"About$

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Use the trigonometric identity cos(A-B) = cos(A)cos(B) + sin(A)sin(B).
\n" ); document.write( "So we have cos(90-a) = cos(90)cos(a) + sin(90)sin(a)
\n" ); document.write( "Since cos(90) = 0, and sin(90) = 1, this simplifies to sin(a).
\n" ); document.write( "Thus, cos(90-a) = sin(a)
\n" ); document.write( "Try an example. Let a = 90.
\n" ); document.write( "cos(90-90) = sin(90), cos(0) = 1 = sin(90). \n" ); document.write( "

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