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2018 WAEC Mathematics Theory (a) The graph of \(y = 2px^{2} - p^{2}x - 14\) passes through the point...

Mathematics
WAEC 2018

(a) The graph of \(y = 2px^{2} - p^{2}x - 14\) passes through the point (3, 10). Find the values of p.

(b) Two lines, \(3y - 2x = 21\) and \(4y + 5x = 5\) intersect at the point Q. Find the coordinates of Q.

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Explanation

(a) \(y = 2px^{2} - p^{2}x - 14\)

At point (3, 10), y = 10 when x = 3.

\(\implies 10 = 2p(3^{2}) - p^{2}(3) - 14\)

\(10 = 18p - 3p^{2} - 14\)

\(-10 = 3p^{2} - 18p + 14 \implies 3p^{2} - 18p + 24 = 0\)

\(3p^{2} - 12p - 6p + 24 = 0\)

\((p - 4)(3p - 6) = 0 \implies \text{p = 2 or 4}\).

(b) \(3y - 2x = 21 ... (1)\)

      \(4y + 5x = 5 ....(2)\)

Using elimination method, multiply (1) by 4 and (2) by 3.

\((1) \times 4 : 12y - 8x = 84 ... (3)\)

\((2) \times 3 : 12y + 15x = 15 ... (4)\)

Subtracting (3) - (4), we have:

\(-23x = 69 \implies x = -3\)

Putting x = -3 in (1), we have

\(3y - 2(-3) = 3y + 6 = 21\)

\(3y = 15 \implies y = 5\)

Hence, the coordinates of Q are (-3, 5).


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