Set 4: Linear Equations (Intermediate)

Choice C is correct. Choice B is the correct answer. This is a special case where the solution is zero. 1. Start with the equation: $x + 9 = 9$ 2. Subtract 9 from both sides: $x = 9 - 9$ 3. Simplify: $x = 0$ 4. Verify: $0+ 9 = 9$ ✓ This problem demonstrates an important concept: zero is a valid solution! When $x = 0$, adding it to any number leaves that number unchanged. Identity Property: This shows the additive identity property: $a + 0 = a$ for any number $a$. Choice C is incorrect because this results from adding instead of subtracting: $9+ 9 = 18$. This is the wrong operation. Choice D is incorrect because this confuses the constant (9) with the solution. Students might think "the same number on both sides means $x$ equals that number", but that's not how equations work. Choice C is incorrect because this might come from dividing: $\frac{9}{9} = 1$. Division is not relevant for solving this addition equation.