why cant black take the pawn on a2

This is Magnus vs. his app on his youtube channel, Magnus does commentary he's white while the app is Black

go to 11:00 minutes....Magnus says he doesn't think black can take the pawn on a2.?? why   black to move

taking the pawn on a2 is threatening mate isn't it... after the take on a2 black would be winning?

https://www.youtube.com/watch?v=pNvVWeHZG00

Whites discovered check on black's king will lead to white capturing the rook on b8, a good move for white although he will lose the knight in the process.

i dont see where white wins the rook on b8, how?

Is this the right position?

anyone of you wants to play wiht me?

yeah...black to move, i dont see why the rook cant take the white a2 pawn?

After Nh3 check black doesn't really have any good responses. The queen can make some checks and then take the b8 rook.

NH3 and then king can just go KH7?

KH7, Qe7, Kg8, then black is fine right?

Yeah you're right, although I'm pretty sure that's winning.

After 5... Kh7 white should not capture the rook, he can give check with the knight first and then capture the rook. Or give another check if it is  neccesary. 

 

I am wondering another thing about this game. At 7:02, why doesn't ...f6 win a piece for black?

Qe4 looks OK.

Thank you!

what about after Qe7....Kh6?

After 1... Rxa2  2. Nh3+Kh7  3. Qe7+ Kh6 ......

        4. Qf8+ leads to checkmate in one further move.

You should be able to work this out. White must give check on every move or will be mated himself. So after 3.... Kh6 , there are only three Queen moves to consider. I only needed to look at Qf8 because it leaves black only two possible moves, both of which lead to mate on the next move.

after qf8 wheres the mate

No disrespect but I don't think chess is for you. To be able to play you need to examine possible moves on the board. This can be difficult for beginners like yourself, but is easier when there are forced lines and limited moves available for either player.

I gave you the moves and if you are unable to look further into the position (mate in one) then I suggest you look for another hobby.