solve 3x square +12x +15=0using by completing square method
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3x² + 12x + 15 = 0
dividing by 3
⇒ (3x² + 12x + 15)/3 = 0
⇒ x² + 4x + 5 = 0
⇒ x² + 4x = -5
⇒ x² + 2×2×x + 2² = -5 + 2²
⇒ (x + 2)² = -5 + 4 = -1
⇒ x + 2 = √-1 = +i, -i
⇒ x = -2-i and -2+i
dividing by 3
⇒ (3x² + 12x + 15)/3 = 0
⇒ x² + 4x + 5 = 0
⇒ x² + 4x = -5
⇒ x² + 2×2×x + 2² = -5 + 2²
⇒ (x + 2)² = -5 + 4 = -1
⇒ x + 2 = √-1 = +i, -i
⇒ x = -2-i and -2+i
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