O-LevelAdditional MathematicsQuadratic functions4037/12 · May/June 2015 · Q14 Marks
Given that the graph of y = (2k+ 5)x² + kx + 1 does not meet the x-axis, find the possible values of k.
- (a)Given that the graph of y = (2k+ 5)x² + kx + 1 does not meet the x-axis, find the possible values of k.[4]
Mark scheme
Marking points from the official mark scheme (May/June 2015). The mark or mark type is shown in brackets.
- M1 use of b² - 4ac, (not as part of quadratic formula unless isolated at a later stage) with correct values for a, b and c
- k²-4(2k+5) (<0)
- k²-8k-20 (<0)
- M1 attempt to obtain critical values
- (k-10)(k+2) (<0)
- A1 correct critical values
- critical values of 10 and -2
- A1 correct range
- -2<k<10
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