To invalidate a patent it is very important to understand that what comes under Anticipation and what comes under Obviousness.
Under the Patent Act, inventors may obtain patents for their inventions provided they are “new and useful”. While “useful” (i.e., the requirement of utility) is a broadly construed concept that presents a low threshold for inventors to clear, the requirement that inventions be “new” is the more demanding hurdle that is articulated as both novelty and non-obviousness. An invention is not novel, i.e., it is anticipated, if every limitation of the claimed invention is found, explicitly or inherently, within a single reference.
If no single reference contains every such limitation, an invention may still be unpatentable if every limitation can be found across a combination of references where one of ordinary skill (in the relevant art) would have reason to combine such references to arrive at the claimed invention. Stated in this manner, novelty is essentially framed as a “subset” of the broader concept of obviousness — the special case in which all of the elements of an invention are found in a single reference instead of across multiple references. As a consequence, if a reference anticipates an invention, it necessarily renders such invention obvious as well. Anticipation becomes, as put by the oft-repeated maxim, the “epitome of obviousness.”
Detailed explanation with cases can be read here
Dennis with PatentlyO fame has also explained it in a very easy manner here
