# If it is given that Sin A = Cos A then calculate Cos 2A?

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If it is given that Sin A = Cos A then calculate Cos 2A?
posted Jan 21, 2015
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## 4 Answers

+2 votes

Best answer

Sin A=Cos A
implies A=45 degress
Cos 2A= Cos 2(45)=Cos 90=0

answer Jan 21, 2015
+4 votes

Ans : 0

Use the the formula.
cos (A+B) = cos A cos B - Sin A Sin B

So in our case :
cos 2A = Cos (A + A)
= cos A cos A - sin A sin A
since: cos A = sin A
so
= cos^2 A - cos^2 A
= 0

answer Jan 21, 2015
+1 vote

Sin A = Cos A

Divide by Cos A gives us Tan A = 1 i.e. A is 45

so Cos 2A is Cos 90 which is zero

answer Jan 21, 2015
0 votes

Use the the formula.
cos (A+B) = cos A cos B - Sin A Sin B

So in our case :
cos 2A = Cos (A + A)
*Sin A = CosA **
implies A=45 degress
Cos 2A= Cos 2(45)=Cos 90=0

so the right answer is zero(0)

answer Mar 3, 2016

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