Question

Write two expressions with positive and negative numbers to be evaluated with a given variable value.
Evaluate one of them correctly and in the other one make an error. For both, clearly explain the steps you used.

Answer 1

Let's assume our variable value is x = 5.

Expression 1: 2x - 3

To evaluate this expression correctly, we substitute the value of x with 5:
2(5) - 3 = 10 - 3 = 7

Explanation: We first multiply the coefficient 2 by the value of x (5), which gives us 10. Then we subtract 3 from the result to get the final output, 7.

Expression 2: -x + 4

To evaluate this expression with an error, we substitute the value of x with 5, but mistakenly change the sign of the variable:
-(5) + 4 = -5 + 4 = -1

Explanation: We mistakenly change the sign of the variable x from positive to negative. The correct expression would be -(-5) + 4. By omitting the second negative sign, we get -5 instead of the correct answer, which should be 1.

Therefore, the correct result for Expression 1 is 7, and the incorrect result for Expression 2 is -1.