(sina)^2+(cosa)^2= 1

Sina/cosa=tana can be solved by these two formulas.

Cosa = 1/4, Sina = (√ 15)/4, Tana = √ 15 (√ this symbol is the root sign).

Question 5, sinx=2cosx

So sinx/cosx=2=tanx

Because (sinx) 2+(cosx) 2 = 1.

So (2cosx) 2+(cosx) 2 = 1.

Cosx = (√ 5)/5，sinx = (2 √ 5)/5。

The eighth question, 1), the original formula =(4tana-2)/(5+3tana)=5/7.

2), the original formula =3/ 10

3), the original formula = 1+2sina*cosa=8/5.

The ninth question, 1), the original formula = 1/2+ 1/2+√2/2 (do it yourself! )

Question 10, 1), the original formula =-cos (π+a) =+(√ 3)/2.

2), the original formula = tan (π+a) =+/-(√ 3)/3.

I don't know if it's ok, just make do with it!