Choose the main technique to prove the following statement:
3 x + 21 = 0 3 x + 21 = 0 3x+21=0 has an integer solution.

Question

Choose the main technique to prove the following statement: 
 3 x + 21 = 0 3 x + 21 = 0 3x+21=0  has an integer solution.

Answer

T1: Direct proof to show  ( p → q ) ≡ T (p 	o q) \equiv T

Answer

T7: Two-step proof to show  ∃ ! x P ( x ) ≡ T \exists ! x P(x) \equiv T

Answer

T6: Constructive proof to show  ∃ x P ( x ) ≡ T \exists x P(x) \equiv T

Answer

T5: Proof by cases to show  ( ( n ⋁ i = 1 p i ) → q ) ≡ T  \displaystyle \left(\left(\bigvee_{i=1}^n p_i ight) 	o q ight) \equiv T

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