C\m các đẳng thức sau :====--...Giúp Mình Với ...
a, \(\sin^2\left(\dfrac{A}{2}\right)+\sin^2\left(\dfrac{B}{2}\right)+\sin^2\left(\dfrac{C}{2}\right)=1+2\sin\left(\dfrac{A}{2}\right)\sin\left(\dfrac{B}{2}\right)\sin\left(\dfrac{C}{2}\right)\)
b. \(\tan\left(\dfrac{A}{2}\right)\tan\left(\dfrac{B}{2}\right)+\tan\left(\dfrac{B}{2}\right)\tan\left(\dfrac{C}{2}\right)+\tan\left(\dfrac{C}{2}\right)\tan\left(\dfrac{A}{2}\right)=1\)
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