ข้อ4)
$$\sum_{\theta = 1}^{90} \sin^2\theta =(\sum_{\theta = 1}^{44} \sin^2\theta +\sum_{\theta = 1}^{44} \cos^2\theta) + \sin^245^{\circ}$$
$$=22+(\frac{\sqrt{2}}{2})^2=22+\frac{1}{2}=22.5$$
ข้อ1)
$$\because 2^3 \equiv 1 \pmod{7} $$
$$ 2^{3\times 20} \equiv 1^{20} \pmod{7}$$
$$\therefore 2^{60} \equiv 1 \pmod{7}$$
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