If the sin 90° is 1, then the cos °=

90° ; 1 over 2

0° ; square root 2 over 2

90° ; square root 3 over 2

0° ; 1

IF we try the first choice, cos (90) is equal to 1 and not 1/2. First choice is then not true. Cosine of 0 is not square root 2 over 2 but instead, 1. The second choice is then not true. From the first choice we know that cosine of 90 is 1 and not square root 3 over 2. We have the last choice to be the answer. Indeed, cosine of zero is 1. 

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