`~rai~`
\(a)A=\sin^235^\circ+\tan22^\circ+\sin^255^\circ-\cot68^\circ+\cos60^\circ\\\quad\quad=\sin^235^\circ+\tan22^\circ+\cos^235^\circ-\tan22^\circ+\cos60^\circ\\\quad\quad=(\sin^235^\circ+\cos^235^\circ)+(\tan22^\circ-\tan22^\circ)+\cos60^\circ\\\quad\quad=1+0+\dfrac{1}{2}\\\quad\quad=1\dfrac{1}{2}.\\b)B=\sin^212^\circ-2\cos^232^\circ+\sin^278^\circ-2\sin^232^\circ\\\quad\quad=(\sin^212^\circ+\sin^278^\circ)-(2\cos^232^\circ+2\sin^232^\circ)\\\quad\quad=(\sin^212^\circ+\cos^212^\circ)-2(\cos^232^\circ+\sin^232^\circ)\\\quad\quad=1-2.1\\\quad\quad=-1.\\c)C=(\sin65^\circ+\cos65^\circ)^2+(\sin65^\circ-\cos65^\circ)^2\\\quad\quad=\sin^265^\circ+2\sin65^\circ+\cos^265^\circ+\sin^265^\circ-2\sin65^\circ\cos65^\circ\\\quad\quad+\cos^265^\circ\\\quad\quad=2\sin^265^\circ+2\cos^265^\circ\\\quad\quad=2(\sin^265+\cos^265^\circ)\\\quad\quad=2.1=2.\\\text{Giải thích:Công thức áp dụng:}\\+)\sin\alpha=\cos(90^\circ-\alpha).\\+)\tan\alpha=\cot(90^\circ-\alpha).\\+)\sin^2\alpha+\cos^2\alpha=1.\)
