waecmaths question:
If ${{U}_{n}}=n({{n}^{2}}+1)$ evaluate U5 – U4
Option A:
18
Option B:
56
Option C:
62
Option D:
80
waecmaths solution:
$\begin{align} & {{U}_{n}}=n({{n}^{2}}+1) \\ & {{U}_{5}}=5({{5}^{2}}+1)=130 \\ & {{U}_{4}}=4({{4}^{2}}+1)=68 \\ & {{U}_{5}}-{{U}_{4}}=130-68 \\ & {{U}_{5}}-{{U}_{4}}=62 \\\end{align}$
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