JAMB 1997 · UME · Q16

Expressions, formulae & change of subject

Find the value of $K$ if $\dfrac{5 + 2r}{(r + 1)(r - 2)}$ expressed in partial fractions is $\dfrac{K}{r - 2} + \dfrac{L}{r + 1}$ , where $K$ and $L$ are constants.

Worked solution (try it first)

Multiply through: $5 + 2r = K(r + 1) + L(r - 2)$ .
Put $r = 2$ so the $L$ term vanishes: $9 = 3K$ .
So $K = 3$ , option A.

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