When \(f(x) = 2x^{3} + mx^{2} + nx + 11\) is divided by \(x^{2} + 5x + 1\), the quotient is \(2x - 5\) and the remainder is \(30x + 16\). Find the values of...

Assessment: WAEC SSCE - Further Mathematics - 2016 (Essay) Subject: Further Mathematics

Question 1 Report

When \(f(x) = 2x^{3} + mx^{2} + nx + 11\) is divided by \(x^{2} + 5x + 1\), the quotient is \(2x - 5\) and the remainder is \(30x + 16\). Find the values of m and n.

Answer Details

By the division identity, dividend = divisor \(\times\) quotient + remainder:

\[ f(x) = (x^2 + 5x + 1)(2x - 5) + (30x + 16). \]

Expand the product:

\[ (x^2+5x+1)(2x-5) = 2x^3 - 5x^2 + 10x^2 - 25x + 2x - 5 = 2x^3 + 5x^2 - 23x - 5. \]

Add the remainder:

\[ f(x) = 2x^3 + 5x^2 - 23x - 5 + 30x + 16 = 2x^3 + 5x^2 + 7x + 11. \]

Compare with \( f(x) = 2x^3 + mx^2 + nx + 11 \):

\[ m = 5, \qquad n = 7. \]

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