Equations: common information
Equality. Identity. Equation (unknowns, roots
of an equation, solving). Equivalent equations.
Equality  two expressions (numerical or literal ones), jointed by sign " = ".
Identity  a valid numerical equality or a literal equality, valid at any numerical values of letters, contained in it.
E x a m p l e s : 1) A
numerical equality 4 · 7 + 2 = 30 is an identity.
2) A literal
equality ( a + b )( a – b ) = a^{2} – b^{2}
is an identity,
because
it is valid at all values of letters, contained in it.
Equation – a literal equality, which is valid ( i.e. it becomes an identity ) only at
some values of letters, contained in it. These letters are called unknowns and the
values, at which an equality is valid – roots of an equation. Procedure of finding
all roots of an equation is called solving. To solve an equation means to find all
its roots. Substitution of each root into an equation instead of unknown converts it into a valid numerical equality (identity).
Two or some equations are called equivalent equations, if they have the same roots.
E x a m p l e : Equations 5x – 25
= 0 and 2x – 7 = 3 are equivalent, because
they have the same root: x = 5 .
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