I tried to use Lagrange's theorem's consequence which is $|HK| = |H||K|$ because $H \cap K = \{e\}$ but it doesnt bring me anywhere, i tried out the definition of normal subgroups as well but it is also lead me nowhere.
This is the proof, which I mostly understand except for one bit:  You have $h_1 \in H_1$ and $h_2 \in H_2$.   We also have $h_1^{-1}(h_2^{-1}h_1h_2) \in H_1$, because $h_2^{-1}h_1h_2 \in h_2^{-1}H_1h_2 = H_1$. Similarly, we have $(h_1^{-1}h_2^{-1}h_1)h_2 \in H_2$. Therefore  $$ h_1^{-1}h_2^{-1}h_1h_2 \in H_1 \cap H_2 = \{1_G\} $$  and so $h_1^{-1}h_2^{-1}h_1h_2 = \{1_G\}$. Let's first multiply everything on the left by $h_1$  $$h_1^{-1}h_2^{-1}h_1h_2 = \{1_G\}$$ $$ h_1 h_1^{-1}h_2^{-1}h_1h_2 = h_1 \{1_G\}$$ $$ h_2^{-1}h_1h_2 = h_1 \{1_G\}$$   Multiply both sides on the left by $h_2$ giving us  $$ h_1h_2 = h_2 h_1 $$  The bit I don't get is right at the beginning. Why is this correct: "We also have $h_1^{-1}(h_2^{-1}h_1h_2) \in H_1$, because $h_2^{-1}h_1h_2 \in h_2^{-1}H_1h_2 = H_1$."
NB: Nvidia has released an official fix; please see ,  and/or .  Upon waking up Ubuntu 16.04 from Suspend, the following graphical glitches appear around all windows, context menus, and similar:      This is currently known to affect the following NVIDIA cards running the proprietary drivers:  NVIDIA GeForce 610M, driver version 375.39, 340.102 NVIDIA GT 630M, driver version 375.39 NVIDIA GTX 650, driver version 375.39 NVIDIA GT 740M, driver version 378.13 NVIDIA GTX 745, unknown driver version NVIDIA GTX 850M, driver version 375.39, 378.13 NVIDIA GT 940M, driver version 375.39 NVIDIA GTX 950M, unknown driver version NVIDIA GTX 960M, driver version 378.13 NVIDIA GTX 970, driver version 375.39 NVIDIA GTX 970M, driver version 375.39 NVIDIA GTX 980 TI, unknown driver version NVIDIA GTX 1060, driver version 375.26, 375.39, 378.09 NVIDIA GTX 1070, driver version 378.09  The above above list has been sourced from reports from other users here on AU,  thread, and  thread. 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