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WAEC 2020 · Paper 1 · Q49

Using the graph of y=2x2+x−1y = 2x^2 + x - 1, if x=−2.5x = -2.5, what is the value of yy on the curve?

xy−3−2−1123−55101520y = 2x2 + x − 1y = 2x + 5
The vertical scale is a quarter of the horizontal scale.

Try it on a graph

Where do the line and the curve meet?

Worked solution (try it first)
  1. Put x=−2.5x = -2.5 into y=2x2+x−1y = 2x^2 + x - 1.
  2. Square first: (−2.5)2=6.25(-2.5)^2 = 6.25, so 2x2=12.52x^2 = 12.5.
  3. So y=12.5−2.5−1=9.0y = 12.5 - 2.5 - 1 = 9.0, option C.

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