Ta có: Qtoả = Qthu
\(\Leftrightarrow\) m.c.\(\Delta\)t1 = m.c.\(\Delta\)t2
\(\Leftrightarrow\) t - t1 = t2 - t
\(\Leftrightarrow\) t - t1 = 2t1 - t
\(\Leftrightarrow\) 28 - t1 = 2t1 - 28
\(\Leftrightarrow\) - t1 - 2t1 = - 28 - 28
\(\Leftrightarrow\) -3t1 = - 56
\(\Leftrightarrow\) t1 \(\approx\) 18,7 oC
Ta có: t2 = 2t1
\(\Leftrightarrow\) t2 = 2 . 18,7 \(\approx\) 37,4 oC