What is the formula of (x1 + x2) & # - 4x1x2?

What is the formula of (x1 + x2) & # - 4x1x2?

The original formula = (x1) ² + (x2) ² + 2 * X1 * x2-4 * X1 * x2
=（x1）²+（X2）²-2*X1*X2
=（X1-X）²
This is a complete square formula

2cosx = SiNx + 1 find x =?

Let t = Tan (x / 2) be replaced by the universal formula
We obtain SiNx = 2T / (1 + T & # 178;), cost = (1-T & # 178;) / (1 + T & # 178;)
∴2(1-t²)/(1+t²)=2t/(1+t²)+1
=>2(1-t²)=2t+1+t² => 3t²+2t-1=0
=>(3t-1) (T + 1) = 0 = > t = 1 / 3 or - 1
That is, Tan (x / 2) = 1 / 3 or - 1
Ψ X / 2 = arctan (1 / 3) + K π or - π / 4 + K π, K is any integer
That is, x = 2arctan (1 / 3) + 2K π or - π / 2 + 2K π, K is any integer