How to convert degrees, minutes and seconds into degrees

How to convert degrees, minutes and seconds into degrees

1 degree = 60 minutes, 1 minute = 60 seconds, 1 degree = 3600 seconds

Given f (x) + 2F (- x) = x ^ 2 + 2x, find f (x)
I wrote this:
If x and - x in the original formula are exchanged, f (- x) + 2F (x) = x ^ 2-2x ①
Then f (x) + 2F (- x) = x ^ 2 + 2x ②
Finally, simultaneous equations are eliminated

F (x) + 2F (- x) = x ^ 2 + 2x ① let x = - x
f(-x)+2f(x)=x^2-2x ②
① - 2 * 2, eliminate f (- x), get
-3f(x)=-x^2+6x
∴f(x)=x^2/3-2x

Who can help?
1. Sina and cosa are two real roots of the equation 2x ^ 2 + 4kx + 3K = 0 about X, then the value of K is?
If Sina / (1 + COSA) = 3, then cosa Sina =?
3. If x belongs to 0 to π / 4, then LG (SiNx + cosx) = 1 / 2 (3lg2-lg5), then cosx SiNx =?
My friend will tell me, please~

First question
According to Weida's theorem, Sina + cosa = - 2K, Sina * cosa = 3K / 2
(sina+cosa)^2=1+2*sina*cosa=1+3k=4k^2
The solution is K1 = - 1 / 4; K2 = 1
And because B ^ 2-4ac > 0
The solution is K3 / 2
So k = 1
The third question
1/2(3lg2-lg5)=1/2lg((2^3/5)^(1/2))=lg((8/5)^(1/2))
That is SiNx + cosx = (8 / 5) ^ (1 / 2)
(SiNx + cosx) ^ 2 = 8 / 5, then 2sinxcosx = 3 / 5
So (cosx SiNx) ^ 2 = 1-2cosxsinx = 2 / 5
So cosx SiNx = (2 / 5) ^ (1 / 2)