You will generally find the last operation is the first thing to undo. Imagine you are computing the equation on a calculator. The last operation you would type is likely to be the first operation to undo. Letâ€™s look at a really big and messy example; try to spot how weâ€™re working backwards to undo it!
Big Messy Example:
Solve for x: 2(x - 1)2 + 3 = 21
Substitute 4 into the original equation:
2â€¢(4-1)2 + 3 = 21
2â€¢32 + 3 = 21
2â€¢9 + 3 = 21
21 = 21 Yes!