Question

Answer 1

2:

1: A=cos12+cos168+cos36+cos144+cos60+cos120+cos90+cos84

=0+0+0+0+cos84=cos84

1:

a: \(A=-sin\left(pi+alpha\right)\cdot cot\left(alpha\right)-cos\left(alpha\right)+cot\left(\dfrac{pi}{2}-alpha\right)\)

\(=sin\left(alpha\right)\cdot\dfrac{cos\left(alpha\right)}{sin\left(alpha\right)}-cos\left(alpha\right)+tan\left(alpha\right)\)

\(=cos\left(alpha\right)-cos\left(alpha\right)+tan\left(alpha\right)\)

=tan alpha

2: B=sina*[-sin(pi-a)]-tana*(-cot(pi+a))+sin^2(a)

=-sin^2a+1+sin^2a

=1