please help me with these questions with explanations! Also, please help me to sketch the graph by pen or pencil of question 1!

1. Let an-y] = 1641:2 - yz. a) Find the standard form equation of the plane tangent to the graph of f at the point (1,2). h) Sketch the graph of f together with the tangent plane. El 24 Find the standard form equation of the plane tangent to the surface at the specied point. 2' f($?y} =Ezn-ya! (11-1) 3- stay} = retrain: - y}, (2, 2} 5. Let S be the left half of the sphere centered at the origin of radius it. Find the equation of the plane tangent to S at the point (1, 2,D). Hint Because this part of the sphere is not a function of a: and y? you'il have to express it as a function of the appropriate variables and adjust the tangent plane formula accordingly