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$$sin^2 \theta + cos^2 \theta = 1 $$
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$$ 1+cot^2 \theta = cosec^2 \theta $$
$$ tan^2 \theta + 1 = sec^2 \theta $$
$$ sin\theta = cos(90-\theta )$$ (90 ͧÈÒäÁèä´éà¢Õ¹¨Ø´)
$$ cos\theta = sin(90-\theta ) $$ (90 ͧÈÒäÁèä´éà¢Õ¹¨Ø´)
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