Concept:A mathematical expression is a combination of numbers, variables, and operations like addition or multiplication. Not every statement about expressions is correct.
Explanation:Check each option:
Option A:
x2+10x+25 can be factored as
(x+5)2, but it is already in its simplest polynomial form. So it is true that it cannot be simplified further (though factoring is a different kind of simplification).
Option B: The definition of a solution is correct — a value that satisfies the equation is called a solution. So this is true.
Option C:
3+4×5 is a valid numerical expression with numbers and operations. Calling it "not a mathematical expression" is false. Hence this option is NOT true.
Option D: Multiplication is a standard operation on expressions, so this is true.
Therefore, the false statement is Option C.
Answer:Option C