Solve for :
Expand the bracket before touching the subtraction. Multiplying each term inside by :
Doing this first means you only have to worry about one sign change, in the next step.
Distribute the leading minus sign across both terms. This is where most sign errors happen: the minus applies to as well, turning it into :
so the equation becomes
Isolate the -term. Subtract from both sides:
Divide by the coefficient.
The division is exact here — with no rounding — which is a strong hint that was chosen deliberately.
Check in the original equation. With : , so , and . Then . Notice the check runs through the original bracket, not the expanded form, so it would also catch a distribution mistake.
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