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0606 P21 - Nov 2025 - Q2 - 3 marks
7054
The diagram shows the graph of \(y=|3x+3|\).
Use a graphical method to solve the inequality \(|3x+3|\geqslant |x-2|\).
Solution
Answer: \(x\leqslant-\dfrac52\) or \(x\geqslant-\dfrac14\).
The inequality
\(|3x+3|\geqslant |x-2|\)
means that the graph of \(y=|3x+3|\) must be on or above the graph of \(y=|x-2|\).
The graph of \(y=|3x+3|\) has vertex at \(x=-1\). The graph of \(y=|x-2|\) has vertex at \(x=2\). The solution changes at the points where the two graphs intersect.
Find one intersection using the left branch of \(y=|x-2|\) and the right branch of \(y=|3x+3|\):
\(3x+3=-(x-2).\)
Thus
\(4x=-1,\)
so
\(x=-\dfrac14.\)
Find the other intersection using the left branch of \(y=|3x+3|\) and the left branch of \(y=|x-2|\):
\(-(3x+3)=-(x-2).\)
So
\(-3x-3=-x+2,\)
which gives
\(-2x=5,\qquad x=-\dfrac52.\)
From the graph, \(|3x+3|\) is greater than or equal to \(|x-2|\) outside the interval between these two intersection points.