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Use the quadratic formula to solve x^2+8x+9=0

What are the solutions to the equation?

Round irrational solutions to the nearest tenth.

x=−1 and x=−8

x = 1 and x=−9

x=−6.6 and x=−1.4

x=−1.2 and x=−6.8


Please explain the answer!

Respuesta :

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none of your options, not via complete the square nor quadratic the formula.

Solve for x over the real numbers:
x^2 + 8 x + 9 = 0

x = (-8 ± sqrt(8^2 - 4×9))/2 = (-8 ± sqrt(64 - 36))/2 = (-8 ± sqrt(28))/2:
x = (-8 + sqrt(28))/2 or x = (-8 - sqrt(28))/2

sqrt(28) = sqrt(4×7) = sqrt(2^2×7) = 2sqrt(7):
x = (2 sqrt(7) - 8)/2 or x = (-2 sqrt(7) - 8)/2

Factor 2 from -8 + 2 sqrt(7) giving 2 (sqrt(7) - 4):
x = 1/22 (sqrt(7) - 4) or x = (-2 sqrt(7) - 8)/2

(2 (sqrt(7) - 4))/2 = sqrt(7) - 4:
x = sqrt(7) - 4 or x = (-2 sqrt(7) - 8)/2

Factor 2 from -8 - 2 sqrt(7) giving 2 (-sqrt(7) - 4):
x = sqrt(7) - 4 or x = 1/22 (-sqrt(7) - 4)

(2 (-sqrt(7) - 4))/2 = -sqrt(7) - 4:

Answer: x = sqrt(7) - 4 or x = -sqrt(7) - 4_____________________________________________________

Solve for x:
x^2 + 8 x + 9 = 0

Subtract 9 from both sides:
x^2 + 8 x = -9

Add 16 to both sides:
x^2 + 8 x + 16 = 7

Write the left hand side as a square:
(x + 4)^2 = 7

Take the square root of both sides:
x + 4 = sqrt(7) or x + 4 = -sqrt(7)

Subtract 4 from both sides:
x = sqrt(7) - 4 or x + 4 = -sqrt(7)

Subtract 4 from both sides:
Answer:  x = sqrt(7) - 4 or x = -4 - sqrt(7)