Showing all necessary working, solve the equation (eˣ + e⁻ˣ)/(eˣ + 1) = 4, giving your answer correct to 3 decimal places.
- Showing all necessary working, solve the equation ex + e-x ex + 1 = 4, giving your answer correct to 3 decimal places.[5]
Mark scheme
Marking points from the official mark scheme (Oct/Nov 2018). The mark or mark type is shown in brackets.
- [B1] Substitute and obtain 3-term quadratic 3u² + 4u - 1 = 0, or equivalent
- [M1] Solve a 3 term quadratic for u
- [A1] Obtain root (√7-2)/3, or decimal in [0.21, 0.22]
- [M1] Use correct method for finding x from a positive value of eˣ
- [A1] Obtain answer x = -1.536 only
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