Lm hộ giúp mk vs ạ khoanh đúng

\(\textbf{Câu 12:}\\x=-10\cos\left(4\pi t-\dfrac{\pi}{4}\right)=10\cos\left(4\pi t-\dfrac{\pi}{4}-\pi\right)\\\Rightarrow \varphi=-\dfrac{3\pi}{4}(rad)\\\longrightarrow D.\\\textbf{Câu 13:}\\x=-8\cos\left(2 t+\dfrac{\pi}{2}\right)=8\cos\left(2 t+\dfrac{\pi}{2}-\pi\right)\\\Rightarrow \varphi=-\dfrac{\pi}{2}(rad)\\\longrightarrow C.\\\textbf{Câu 14:}\\t=0,25(s)\Rightarrow x=2\cos\left(2\pi.0,25-\dfrac{\pi}{6}\right)=1(cm)\\\longrightarrow A.\\\textbf{Câu 15:}\\t=1(s)\Rightarrow \omega t+\varphi=\pi+\dfrac{\pi}{2}=\dfrac{3\pi}{2}(rad)\\\longrightarrow C.\\\textbf{Câu 16:}\\\omega t+\varphi =\dfrac{2\pi}{3}\Rightarrow x=6\cos\dfrac{2\pi}{3}=-3\\\longrightarrow C.\)