In trigonometry, trigonometric identities are equalities that involve trigonometric functions and are true for every value of the occurring variables for which both sides of the equality are defined. Geometrically, these are identities involving certain functions of one or more angles.

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二倍角公式是数学三角函数中常用的一组公式，通过角α的三角函数值的一些变换关系来表示其二倍角2α的三角函数值，二倍角公式包括正弦二倍角公式、余弦二倍角公式以及正切二倍角公式。 在计算中可以用来化简计算式、减少求三角函数的次数，在工程中也有广泛的运用。

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sin2是指正弦函数的平方，可以表示为sin^2(x)或sin(x)^2。计算sin^2(x)的方法是先计算sin(x)，然后将结果平方。 例如，要计算sin^2(30°)，首先计算sin(30°)： sin(30°) = 0.5 然后将结果平方： sin^2(30°) = (0.5)^2 = 0.25 所以sin^2(30°)等于0.25。

Sin squared x means sin x whole squared. There is two sin squared x formulas. One of them is derived from one of the Pythagorean identities and the other is derived from the double angle formula of the cosine function. The former is used in proving various trigonometric identities whereas the latter is widely used in solving the integrals.

Sin 2x formula is one of the double angle formulas in trigonometry. Using this formula, we can find the sine of the angle whose value is doubled.

As many people have pointed out by now, $\sin^2 x$ is simply a "nickname" for $(\sin x)^2$. Therefore, $\sin^2\ 30 = (\sin 30)^2 = (1/2)^2 = 1/4$. As it happens, though, there is another useful thing we can say about $\sin^2 x$:

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2017年2月24日 · Sin 2 = sin 114.59156 degrees. Our results of sin2 have been rounded to five decimal places. If you want sine 2 with higher accuracy, then use the calculator below; our tool displays ten decimal places.