Check the equation on the way to determine the pH of seawater.

From

   [H₂CO₃] = [H⁺]²・[DIC]/ ([H⁺]² + K_1[H^+] + K₁K₂)   　equation (7)

　pCO₂ =[H₂CO₃]／K₀ 　   equation (2)

　pCO₂ = { [H⁺]²・[DIC]/ ([H⁺]² + K₁[H⁺] + K₁K₂) }／K₀

 Transform the equation,

( [H⁺]² + K₁[H⁺] + K₁K₂) ・K₀・pCO₂ = [H⁺]²・[DIC]

 (K₀・pCO₂ －[DIC])[H⁺]² + K₁・K₀・pCO₂ ・[H⁺]+ K₁K₂K₀・pCO₂ = 0

Solve the quadratic equation for this [H+].

It is a lengthy process, but please use paper and pencil and calculate carefully.

(At this stage, the ± in front of the root cannot be determined, but assign a numerical value and choose the one that is positive.)