Kai Chew's answer to Ricky's Secondary 3 A Maths Singapore question.
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y = -5x^2 + 20x +c
since ball reach a height of less than 50m,
50>height of ball
50>-5x^2 +20x +c
0>-5x^2+20x+c -50
since curve is completely below the x-axis, curve has no real roots, hence, b^2 - 4ac < 0
20^2 - 4(-5)(c-50)<0
400+20(c-50)<0
400+20c-1000<0
20c<600
c<30
since ball reach a height of less than 50m,
50>height of ball
50>-5x^2 +20x +c
0>-5x^2+20x+c -50
since curve is completely below the x-axis, curve has no real roots, hence, b^2 - 4ac < 0
20^2 - 4(-5)(c-50)<0
400+20(c-50)<0
400+20c-1000<0
20c<600
c<30
Date Posted:
1 year ago
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