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Mathematics

The value (values) of x satisfying the equation x2 - 6x - 16 = 0 is/are :

  1. 8 or -2

  2. -8 or 2

  3. 8 and -2

  4. -8 or 2

Quadratic Equations

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Answer

Comparing equation x2 - 6x - 16 = 0 with ax2 + bx + c = 0, we get :

a = 1, b = -6 and c = -16.

By formula,

x = b±b24ac2a\dfrac{-b \pm \sqrt{b^2 - 4ac}}{2a}

Substituting values we get :

x=(6)±(6)24×1×162×1=6±36+642=6±1002=6±102=6+102 or 6102=162 or 42=8 or 2.x = \dfrac{-(-6) \pm \sqrt{(-6)^2 - 4 \times 1 \times -16}}{2 \times 1} \\[1em] = \dfrac{6 \pm \sqrt{36 + 64}}{2} \\[1em] = \dfrac{6 \pm \sqrt{100}}{2} \\[1em] = \dfrac{6 \pm 10}{2} \\[1em] = \dfrac{6 + 10}{2} \text{ or } \dfrac{6 - 10}{2} \\[1em] = \dfrac{16}{2} \text{ or } \dfrac{-4}{2} \\[1em] = 8 \text{ or } -2.

Substituting x = 8 in L.H.S. of equation x2 - 6x - 16 = 0, we get :

⇒ 82 - 6(8) - 16

⇒ 64 - 48 - 16

⇒ 0.

Substituting x = -2 in L.H.S. of equation x2 - 6x - 16 = 0, we get :

⇒ (-2)2 - 6(-2) - 16

⇒ 4 + 12 - 16

⇒ 0.

Since, L.H.S. = R.H.S., thus x = -2 is a solution of the equation.

Thus 8 and -2 are the solution of the equation x2 - 6x - 16 = 0.

Hence, Option 3 is the correct option.

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