Source: NJC 2015 Junior High 3 MA301 YEA Q4, sent by one of my Y3 students
A good example of a simultaneous equation question that teaches important skills which are used in Y5/Y6 or Senior High.
In part ii, the keyword hence is used. Most students stumble at this question as they try to solve part ii by redo-ing the simultaneous equation. Part i is generally solvable by most IP students.
The trick here is to use the solutions for x and y that you have given in part i. Looking at part ii, 9(a+1)^2 + 4b^2 = 18 looks almost exactly like the equation given in part i. You can safely conclude that you should substitute x=a+1 and y=2b as they expand with square to give you the same equation you have in part ii. Sub x=a+1 and y=2b into the other equation in part ii, and do some simple expansion to manipulate it to look like 2x + y = 5. Afterwords, sub x=a+1 and y=2b into the solutions of part i, and you have your answer.
I hope this has been helpful to your revision, and good luck for your exams
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