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18 December, 08:09

If y=x^2+8x+9, what's the 2 x-intercepts of the parabola?

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  1. 18 December, 08:43
    0
    x = - 4 ±√ (7)

    or in decimal:

    x = - 1.35 or - 6.65

    Step-by-step explanation:

    y=x²+8x+9

    note x-intercepts occur when y = 0,

    Hence, x²+8x+9 = 0 (solve this using your favorite method. We will complete the square)

    x²+8x+9 = 0 (rearrange)

    x²+8x = - 9 (complete the square and add factor to both sides)

    x² + 8x + (8/2) ² = - 9 + (8/2) ²

    [ x + (8/2) ]² = - 9 + (8/2) ²

    [ x + 4 ]² = - 9 + (4) ²

    [ x + 4 ]² = - 9 + 16

    [ x + 4 ]² = 7

    x+4 = ±√ (7)

    x = - 4 ±√ (7)

    x = - 1.35 or - 6.65
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