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Which line correctly expands the left-hand side of ?

Class 7Simple EquationsSimple Equations
  • A
  • B
  • C
  • D

Step-by-Step Solution

The 5 outside multiplies EVERY term inside the bracket: and , so . Finishing: → , and ✓. Writing forgets to distribute across the −3, the commonest bracket slip; loses the minus sign; adds where it should multiply.
Answer: C)

Key idea: The balance principle

An equation is like a balance scale: LHS on one pan, RHS on the other, and the scale is level. Whatever you do to one side, you must do to the other to keep it balanced. So if you add 5 to LHS, add 5 to RHS. If you divide LHS by 3, divide RHS by 3.

Goal: isolate the variable on one side. Get by itself by undoing every operation around it, in reverse order, applied to BOTH sides.

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