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The style of artists changes with age. Although they are all by Vincent van Gogh ( Dutch, 1853-890), the first has a slightly different style. The colors are different. The impasto is the same. The brush strokes make short thick lines in all three, but in the first they are straight while the last two are swirling.

2 Rembrandt Harmensz. van Rijn 053.jpg

Although they are all by Rembrandt van Rijn (Dutch, 1606–1669), the first two have a similar color pallet with heavy impasto. The last painting doesn't use impasto because that would make it look less real, more like a painting, and less disturbing.
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The first is by Monet while the last two are by van Gogh. This one is difficult because the subject is similar in the first two while the colors are similar in all three. They are all impressionistic, so in that sense the style is the same, but take a closer look at the brush strokes. Look at how Monet's bleed into the canvass. Look at how he outlines the lilies with continuous lines. There is a serenity to it.
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 Jan van Eyck (Flemish, 1395–1441) is the artist of all three. All have great realism - and lush velvet clothing, but the last has a subject matter that looks like Hieronymus Bosch (Dutch, 450-1516). What is different about the Bosh?
5

Pierre-Auguste Renoir (French, 1841–1919) painted the first two, and Mary Cassatt (1844 – 1926) was American, but she worked in France during the impressionistic movement. The last painting is a Cassatt. Strangely enough her work is very much like Renoir, but this painting is different. Notice the flat solid colored areas with drypoint shading. It looks unfinished; only the hair looks finished. 
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Amadeo Modigliani 064.jpg

Amadeo Modigliani 008.jpg Amedeo Modigliani (Italian, 1884 – 1920) also lived in France. An obvious stylistic trait are the elongated elegant shapes. The eyes are usually blocked in, with warm tones, and simple backgrounds.
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The first is by Andy Warhol (American, 1928 – 1987). Center is by David Hockney  (English, 1937 ). It is actually similar to the Cassatt in its flat surfaces. Flag by Jasper Johns  (American, 1930). It has a pop art subject although he is no a pop artist - with a thick impasto texture.