2(xy)
y=2x
If the expression is (x - y)2, the solution is (7 - -2)2 = (7+2)2 = 92 = 81. If the expression is x - y2, the solution is 7 - (-2)2 = 7 - 4 = 3.
A mathematical expression in its' most simplistic form, merely assigns a value to a variable. Don't confuse an expression with an equation. An equation requires a solution. An expression cannot be "solved". It only allows you to determine the value of a variable. This is the expression in words "x is equal to 3" (X is the variable which is equal to the constant number 3) This is the expression in numbers "x=3" The expression in words "y is equal to 6" (Y is the variable which is equal to the constant number 6) The expression in numbers is "y=6" I hope you understand now.
y - x - 3 is an expression, not an equation nor an inequality. It cannot, therefore, have a solution.
You can only get a specific number for an expression if you assign numbers to the variables. As an expression, the existing expression cannot be simplified.
y - 5x
x times y or, symbolically, either x*y or simply xy (where context allows, also X x Y)
7 + x
yz - x
Twice the sum of 'x' and 'y' . . . 2(x+y) The sum of twice 'x' and 'y' . . . (2x+y)
x / (2y - 7)
3(2y)(x)6xy
2(x+y) is twice the sum of x and y, and 2x+y is the sum of twice x and y
0.5*xy
4(x+y)
This phrase might be represented by the mathematical expression Y + (-5x). Because there is no additional information, you cannot determine what either Y or x is.
X = 15 - 5y