Đáp án:

 `A=9`

Giải thích các bước giải:

 `A=sin^{2}10^{o}+sin^{2}20^{o}+...+sin^{2}180^{o}`

`=(sin^{2}10^{o}+sin^{2}170^{o})+(sin^{2}20^{o}+sin^{2}160^{o})+(sin^{2}30^{o}+sin^{2}150^{o})+(sin^{2}40^{o}+sin^{2}140^{o})+(sin^{2}50^{o}+sin^{2}130^{o})+(sin^{2}60^{o}+sin^{2}120^{o})+(sin^{2}70^{o}+sin^{2}110^{o})+(sin^{2}80^{o}+sin^{2}110^{o})+sin^{2}90^{o}+sin^{2}180^{o}`

`->A=(sin^{2}10^{o}+cos^{2}10^{o})+(sin^{2}20^{o}+cos^{2}20^{o})+(sin^{2}30^{o}+cos^{2}30^{o})+(sin^{2}40^{o}+cos^{2}40^{o})+(sin^{2}50^{o}+cos^{2}50^{o})+(sin^{2}60^{o}+cos^{2}60^{o})+(sin^{2}70^{o}+cos^{2}70^{o})+(sin^{2}80^{o}+cos^{2}80^{o})+1+0`

`=1+1+...+1` (có `9` số `1`)

`=9`

Vậy `A=9`