Ta có:a^{4 m}b^{4 m}-(a ^mb ^m+1)(a^{2 m}b^{2 m}+1)(a ^mb ^m-1)

   =  a^{4 m}b^{4 m}-(a ^2mb ^2m-1)(a^{2 m}b^{2 m}+1)

   =  a^{4 m}b^{4 m}-(a ^4mb ^4m-1)

   = 1

31. They recommend (walk)___________walking______ around the lake
32. They recommend me (walk)_____to walk____________ around the lake
33. They encourage us (do)_______to do______ the test
34. They encourage (do)_______doing_______ the test
35. He denied (have)_______having_________ been there.
36. His plan is (keep)_______keep_______ the affair secret. 
37. It seems impossible (save)______to save______ money 

38. It’s time we (water)______watered________ the flowers in the garden
39. The guest had the porters (carry) _______ carried________ their luggage upstairs.
40. We incidentally saw the plane (crash)____crashing___________ into the mountain.
41. The man noticed his assistant (leave)_____leaving________ work earlier than usual.
42. They stopped (look)_______to look___ at the pictures.
43. They stopped (smoke) ____smoking_________ because it is bad for their
health.
44. The water in this glass is too hot (drink)_______to drink________.
45. It’s high time we (go)_________went____ to work
46. They speak slowly enough for me (understand)_______to understand________.

C.NO.