A variable is a letter that represents unspecified numbers e.g. x, y or z.
To evaluate an algebraic expression you have to substitute each variable with a number and perform the operations included.
If we know the value of our variables we can substitute the variables for their values and thus evaluate the expression
Calculate if x=3 and z=2
Replace x with 3 and z with 2 to evaluate the expression.
Video lesson: Evaluate the following expression for x = 2, y = 5 and z = 4
The solution can be seen in the video in the next page.
Here we have an algebraic equation rather than an expression that we want to evaluate for values of x, y and z and see what we get. The expression is 4x+(7-z)-6y. Now if we’re given values for x, z and y then we can evaluate this expression to some numerical value. We’re given x=2, z=4 and y=5. So here we have our values of x,z and y so we can just plug in our evaluate for those three values. So here we have four times two plus seven minus z is four and minus six times y which is five. Now we can just multiply these out and simplify a little bit from here. Four times two is eight, plus seven minus four is three. Minus six times five is thirty. Now we can add these, eight plus three is eleven minus thirty. Eleven minus thirty is negative nineteen.