Expression B: 3x + 10y
Expression A: 7x - 4y
Step-by-step explanation:
The difference in calculation of expression A vs expression B is due to the signs in between the parenthesis in both expression respectively. The sign of the 2nd parenthesis in expression B will change because of the the negative sign before it. While that of the 2nd expression in A will remain the same because of the positive sign.
Expression B: (5x + 3y) - (2x - 7y)
To solve this, we need to expand the parenthesis:
5x + 3y -(2x) -(-7y)
Multiplication of same sign gives positive number. Multiplication of opposite signs give negative number.
5x + 3y -2x + 7y
collect like terms:
5x-2x + 3y + 7y
= 3x + 10y
Expression A: (5x + 3y) + (2x - 7y)
To solve this, we need to expand the parenthesis:
5x + 3y +(2x) + (-7y)
Multiplication of same sign gives positive number. Multiplication of opposite signs give negative number.
5x + 3y + 2x - 7y
collect like terms:
5x +2x +3y -7y
= 7x - 4y