Test Index

JAMB Mathematics 2014 Paper

Question : 6

Total: 47

Solve for x in 8x^-2 = 2/25

Solution:

Concept:

Use the negative exponent rule and then solve the resulting quadratic equation.

Explanation:

Start with

8x^{-2} = \frac{2}{25}

Divide both sides by

8

x^{-2} = \frac{2}{25 \times 8} = \frac{2}{200} = \frac{1}{100}

Since

x^{-2} = \frac{1}{x^2}

, write:

\frac{1}{x^2} = \frac{1}{100}

Invert both sides to get

x^2 = 100

Taking the square root gives

x = \pm 10

From the options, the correct positive value is

x = 10

Answer:

10

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