Work out the sum sin²5° + sin²10° + sin²15° + … + sin²90°.

9 1/2. 18 terms. Pairs (5^°,85^°), ,(40^°,50^°) give 8; ^2 45^° = 12; ^2 90^° = 1. Total 9 12.

Work out the sum si $n^{2}$ 5° + si $n^{2}$ 10° + si $n^{2}$ 15° + … + si $n^{2}$ 90°.

Competition practiceTrigonometry

18 terms. Pairs

(5^{\circ}, 8 5^{\circ}), \dots, (4 0^{\circ}, 5 0^{\circ})

give 8;

sin^{2} 4 5^{\circ} = \frac{1}{2}

;

sin^{2} 9 0^{\circ} = 1

. Total

9 \frac{1}{2}

Answer: A) 9 1/2

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